This material is based upon work supported by the National Science Foundation under Grant MCB-1817448 and by an award from the Thomas F. and Kate Miller Jeffress Memorial Trust, Bank of America, Trustee and specified donor Hazel Thorpe Carman and George Gay Carman Trust.

1. Assay component preparation
<ol>
	<li>Determine the chromatography fractions to be assayed using optical absorbance at 280 nm or alternative methods of protein quantification to identify the protein enriched fractions. 
	NOTE: For this work, we used a diode array UV-Vis spectrophotometer. To increase throughput, a plate reader capable of measuring UV-Vis absorbance can be used.</li>
	<li>Preparation of necessary assay components
	<ol>
		<li>Prepare or obtain 10-100 mM buffer (&#34;Sample Buffer&#34;) with a pH ...

<ol>
	<li>Porath, J., Carlsson, J. A. N., Olsson, I., Belfrage, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal+chelate+affinity+chromatography,+a+new+approach+to+protein+fractionation.">Metal chelate affinity chromatography, a new approach to protein fractionation.</a> Nature. 258 (5536), 598-599 (1975).</li><li>Block, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immobilized-Metal+Affinity+Chromatography+(IMAC):+A+Review.">Immobilized-Metal Affinity Chromatography (IMAC): A Review.</a> Methods in Enzymology. 463, 439-473 (2009).</li><li>Takeda, N., Matsuoka, T., Gotoh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potentiality+of+IMAC+as+sample+pretreatment+tool+in+food+analysis+for+veterinary+drugs.">Potentiality of IMAC as sample pretreatment tool in food analysis for veterinary drugs.</a> Chromatographia. 72 (1/2), 127-131 (2010).</li><li>Felix, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+serum+proteins+involved+in+pancreatic+cancer+cachexia.">Identification of serum proteins involved in pancreatic cancer cachexia.</a> Life sciences. 88 (5-6), 218-225 (2011).</li><li>Wu, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+enhanced+laser+desorption/ionization+profiling:+New+diagnostic+method+of+HBV-related+hepatocellular+carcinoma.">Surface enhanced laser desorption/ionization profiling: New diagnostic method of HBV-related hepatocellular carcinoma.</a> Journal of Gastroenterology and Hepatology. 24 (1), 55-62 (2009).</li><li>Goldsmith, J. O., Boxer, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+isolation+of+bacterial+photosynthetic+reaction+centers+with+an+engineered+poly-histidine+tag.">Rapid isolation of bacterial photosynthetic reaction centers with an engineered poly-histidine tag.</a> Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1276 (3), 171-175 (1996).</li><li>Guergova-Kuras, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+and+one-step+purification+of+a+fully+active+polyhistidine-tagged+cytochrome+bc1+complex+from+Rhodobacter+sphaeroides.">Expression and one-step purification of a fully active polyhistidine-tagged cytochrome bc1 complex from Rhodobacter sphaeroides.</a> Protein Expression and Purification. 15 (3), 370-380 (1999).</li><li>Mitchell, D. M., Gennis, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+purification+of+wildtype+and+mutant+cytochrome+c+oxidase+from+Rhodobacter+sphaeroides+by+Ni(2+)-NTA+affinity+chromatography.">Rapid purification of wildtype and mutant cytochrome c oxidase from Rhodobacter sphaeroides by Ni(2+)-NTA affinity chromatography.</a> FEBS Letters. 368 (1), 148-150 (1995).</li><li>Tian, H., White, S., Yu, L., Yu, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+the+head+domain+movement+of+the+rieske+iron-sulfur+protein+in+electron+transfer+reaction+of+the+cytochrome+bc1+complex.">Evidence for the head domain movement of the rieske iron-sulfur protein in electron transfer reaction of the cytochrome bc1 complex.</a> Journal of Biological Chemistry. 274 (11), 7146-7152 (1999).</li><li>Tian, H., Yu, L., Mather, M. W., Yu, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexibility+of+the+neck+region+of+the+rieske+iron-sulfur+protein+is+functionally+important+in+the+cytochrome+bc1+complex.">Flexibility of the neck region of the rieske iron-sulfur protein is functionally important in the cytochrome bc1 complex.</a> Journal of Biological Chemistry. 273 (43), 27953-27959 (1998).</li><li>Louie, A. Y., Meade, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal+complexes+as+enzyme+inhibitors.">Metal complexes as enzyme inhibitors.</a> Chemical Reviews. 99 (9), 2711-2734 (1999).</li><li>Tam&#225;s, M. J., Sharma, S. K., Ibstedt, S., Jacobson, T., Christen, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heavy+Metals+and+Metalloids+As+a+Cause+for+Protein+Misfolding+and+Aggregation.">Heavy Metals and Metalloids As a Cause for Protein Misfolding and Aggregation.</a> Biomolecules. 4 (1), 252-267 (2014).</li><li>Gerencser, L., Maroti, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retardation+of+proton+transfer+caused+by+binding+of+the+transition+metal+ion+to+the+bacterial+reaction+center+is+due+to+pKa+shifts+of+key+protonatable+residues.">Retardation of proton transfer caused by binding of the transition metal ion to the bacterial reaction center is due to pKa shifts of key protonatable residues.</a> Biochemistry. 40 (6), 1850-1860 (2001).</li><li>Klishin, S. S., Junge, W., Mulkidjanian, A. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flash-induced+turnover+of+the+cytochrome+bc1+complex+in+chromatophores+of+Rhodobacter+capsulatus:+binding+of+Zn2++decelerates+likewise+the+oxidation+of+cytochrome+b,+the+reduction+of+cytochrome+c1+and+the+voltage+generation.">Flash-induced turnover of the cytochrome bc1 complex in chromatophores of Rhodobacter capsulatus: binding of Zn2+ decelerates likewise the oxidation of cytochrome b, the reduction of cytochrome c1 and the voltage generation.</a> Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1553 (3), 177-182 (2002).</li><li>Link, T. A., von Jagow, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zinc+ions+inhibit+the+QP+center+of+bovine+heart+mitochondrial+bc1+complex+by+blocking+a+protonatable+group.">Zinc ions inhibit the QP center of bovine heart mitochondrial bc1 complex by blocking a protonatable group.</a> Journal of Biological Chemistry. 270 (42), 25001-25006 (1995).</li><li>Block, H., Kubicek, J., Labahn, J., Roth, U., Sch&#228;fer, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+and+comprehensive+quality+control+of+recombinant+human+Interleukin-1beta:+a+case+study+for+a+process+development+strategy.">Production and comprehensive quality control of recombinant human Interleukin-1beta: a case study for a process development strategy.</a> Protein Expression and Purification. 57 (2), 244-254 (2008).</li><li>Kokhan, O., Shinkarev, V. P., Wraight, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binding+of+imidazole+to+the+heme+of+cytochrome+c1+and+inhibition+of+the+bc1+complex+from+Rhodobacter+sphaeroides:+II.+Kinetics+and+mechanism+of+binding.">Binding of imidazole to the heme of cytochrome c1 and inhibition of the bc1 complex from Rhodobacter sphaeroides: II. Kinetics and mechanism of binding.</a> Journal of Biological Chemistry. 285 (29), 22522-22531 (2010).</li><li>Kokhan, O., Shinkarev, V. P., Wraight, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binding+of+imidazole+to+the+heme+of+cytochrome+c1+and+inhibition+of+the+bc1+complex+from+Rhodobacter+sphaeroides:+I.+Equilibrium+and+modeling+studies.">Binding of imidazole to the heme of cytochrome c1 and inhibition of the bc1 complex from Rhodobacter sphaeroides: I. Equilibrium and modeling studies.</a> Journal of Biological Chemistry. 285 (29), 22513-22521 (2010).</li><li>Bornhorst, J. A., Falke, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+proteins+using+polyhistidine+affinity+tags.">Purification of proteins using polyhistidine affinity tags.</a> Methods in Enzymology. 326, 245-254 (2000).</li><li>Kokhan, O., Marzolf, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+and+quantification+of+transition+metal+leaching+in+metal+affinity+chromatography+with+hydroxynaphthol+blue.">Detection and quantification of transition metal leaching in metal affinity chromatography with hydroxynaphthol blue.</a> Analytical Biochemistry. 582, 113347 (2019).</li><li>Doyle, C., Naser, D., Bauman, H., Rumfeldt, J., Meiering, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectrophotometric+method+for+simultaneous+measurement+of+zinc+and+copper+in+metalloproteins+using+4-(2-pyridylazo)resorcinol.">Spectrophotometric method for simultaneous measurement of zinc and copper in metalloproteins using 4-(2-pyridylazo)resorcinol.</a> Analytical Biochemistry. 579, 44-56 (2019).</li><li>Furrer, J., Smith, G. S., Therrien, B., Gasser, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Inorganic Chemical Biology. , (2014).</li><li>Hogeling, S. M., Cox, M. T., Bradshaw, R. M., Smith, D. P., Duckett, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+proteins+in+whole+blood,+plasma+and+DBS,+with+element-labelled+antibody+detection+by+ICP-MS.">Quantification of proteins in whole blood, plasma and DBS, with element-labelled antibody detection by ICP-MS.</a> Analytical Biochemistry. 575, 10-16 (2019).</li><li>Yamasaki, S., Tsumura, A., Takaku, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultratrace+Elements+in+Terrestrial+Water+as+Determined+by+High-Resolution+ICP-MS.">Ultratrace Elements in Terrestrial Water as Determined by High-Resolution ICP-MS.</a> Microchemical Journal. 49 (2), 305-318 (1994).</li><li>Brittain, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complex+Formation+Between+Hydroxy+Naphthol+Blue+and+First+Row+Transition+Metal+Cyanide+Complexes.">Complex Formation Between Hydroxy Naphthol Blue and First Row Transition Metal Cyanide Complexes.</a> Analytical Letters. 10 (13), 1105-1113 (1977).</li><li>Brittain, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binding+of+Transition+Metal+Ions+by+the+Calcium+Indicator+Hydroxy+Naphthol+Blue.">Binding of Transition Metal Ions by the Calcium Indicator Hydroxy Naphthol Blue.</a> Analytical Letters. 11 (4), 355-362 (1978).</li><li>Temel, N. K., Sertakan, K., G&#252;rkan, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preconcentration+and+Determination+of+Trace+Nickel+and+Cobalt+in+Milk-Based+Samples+by+Ultrasound-Assisted+Cloud+Point+Extraction+Coupled+with+Flame+Atomic+Absorption+Spectrometry.">Preconcentration and Determination of Trace Nickel and Cobalt in Milk-Based Samples by Ultrasound-Assisted Cloud Point Extraction Coupled with Flame Atomic Absorption Spectrometry.</a> Biological Trace Element Research. 186 (2), 597-607 (2018).</li><li>Ferreira, S. L. C., Santos, B. F., de Andrade, J. B., Costa, A. C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectrophotometric+and+derivative+spectrophotometric+determination+of+nickel+with+hydroxynaphthol+blue.">Spectrophotometric and derivative spectrophotometric determination of nickel with hydroxynaphthol blue.</a> Microchimica Acta. 122 (1), 109-115 (1996).</li><li>Denisov, I. G., Grinkova, Y. V., Lazarides, A. A., Sligar, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+Self-Assembly+of+Monodisperse+Phospholipid+Bilayer+Nanodiscs+with+Controlled+Size.">Directed Self-Assembly of Monodisperse Phospholipid Bilayer Nanodiscs with Controlled Size.</a> Journal of the American Chemical Society. 126 (11), 3477-3487 (2004).</li><li>Grinkova, Y. V., Denisov, I. G., Sligar, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+extended+membrane+scaffold+proteins+for+self-assembly+of+soluble+nanoscale+lipid+bilayers.">Engineering extended membrane scaffold proteins for self-assembly of soluble nanoscale lipid bilayers.</a> Protein Engineering, Design and Selection. 23 (11), 843-848 (2010).</li><li>Bonta, M., Hegedus, B., Limbeck, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+dried-droplets+deposited+on+pre-cut+filter+paper+disks+for+quantitative+LA-ICP-MS+imaging+of+biologically+relevant+minor+and+trace+elements+in+tissue+samples.">Application of dried-droplets deposited on pre-cut filter paper disks for quantitative LA-ICP-MS imaging of biologically relevant minor and trace elements in tissue samples.</a> Analytica Chimica Acta. 908, 54-62 (2016).</li><li>Olmedo, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validation+of+a+method+to+quantify+chromium,+cadmium,+manganese,+nickel+and+lead+in+human+whole+blood,+urine,+saliva+and+hair+samples+by+electrothermal+atomic+absorption+spectrometry.">Validation of a method to quantify chromium, cadmium, manganese, nickel and lead in human whole blood, urine, saliva and hair samples by electrothermal atomic absorption spectrometry.</a> Analytica Chimica Acta. 659 (1), 60-67 (2010).</li><li>Shyamal, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Selective+Turn-On+Fluorogenic+Chemosensor+for+Robust+Quantification+of+Zn(II)+Based+on+Aggregation+Induced+Emission+Enhancement+Feature.">Highly Selective Turn-On Fluorogenic Chemosensor for Robust Quantification of Zn(II) Based on Aggregation Induced Emission Enhancement Feature.</a> ACS Sensors. 1 (6), 739-747 (2016).</li><li>Kudo, H., Yamada, K., Watanabe, D., Suzuki, K., Citterio, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paper-Based+Analytical+Device+for+Zinc+Ion+Quantification+in+Water+Samples+with+Power-Free+Analyte+Concentration.">Paper-Based Analytical Device for Zinc Ion Quantification in Water Samples with Power-Free Analyte Concentration.</a> Micromachines. 8 (4), 127 (2017).</li><li>Liu, R., Zhang, P., Li, H., Zhang, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lab-on-cloth+integrated+with+gravity/capillary+flow+chemiluminescence+(GCF-CL):+towards+simple,+inexpensive,+portable,+flow+system+for+measuring+trivalent+chromium+in+water.">Lab-on-cloth integrated with gravity/capillary flow chemiluminescence (GCF-CL): towards simple, inexpensive, portable, flow system for measuring trivalent chromium in water.</a> Sensors and Actuators B: Chemical. 236 (C), 35-43 (2016).</li></ol>

Colorimetric detection of metals using HNB provides a simple way to quantify the degree of protein contamination by transition metal ions from IMAC resins. As we established in Ref. 20, Ni2+ binds to HNB with 1:1 stoichiometry and the dissociation constant for the Ni-HNB complex changes with pH. However, the complex Kd is in the sub-nM range for all recommended (7-12) pH values. In practical terms, it means that all Ni2+ in any tested fractions will bind to HNB as long as no other strong ...

Since its inception by Porath and co-workers1, immobilized metal affinity chromatography (IMAC) has become a method of choice to quickly separate proteins based on their ability to bond with transition metal ions such as Zn2+, Ni2+, Cu2+, and Co2+. This is most commonly done via engineered poly-histidine tags and is now one of the most common chromatographic purification techniques for the isolation of recombinant proteins2. IMAC has also found applications beyond recombinant protein purification as a way to isolate quinolones, tetracyclines, aminoglycosides, macrolides, and &#946;-lactams for food sample analysis3 and as a step in identifying blood-serum protein markers for liver and pancreatic cancers4,5. Not surprisingly, IMAC has also become a method of choice for the isolation of a number of native bioenergetics enzymes6,7,8,9,10. However, successful implementation of these purification methods for studies on enzymatically active bioenergetic proteins is dependent on the presence of negligible levels of metal cations leached from the column matrix into the eluate. The divalent metal cations commonly used in IMAC have known pathologic biological significance, even at low concentrations11,12. The physiological effect of these metals is most pronounced in bioenergetic systems, where they can prove lethal as inhibitors of cellular respiration or photosynthesis13,14,15. Similar issues are unavoidable for the majority of protein classes where residual contaminant metals can interfere with a protein&#39;s biological functions or characterization with biochemical and biophysical techniques.
While the levels of metal contamination under oxidizing conditions and using imidazole as an eluant are typically low16, protein isolations performed in the presence of cysteine reducing agents (DTT, &#946;-mercaptoethanol, etc.) or with stronger chelators like histidine17,18 or ethylenediaminetetraacetic acid (EDTA) result in much higher levels of metal contamination19,20. Similarly, since metal ions in IMAC resins are frequently coordinated by carboxylic groups, protein elutions performed under acidic conditions are also likely to have much higher levels of metal contamination. Metal content in solutions can be assessed using atomic absorption spectroscopy (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS) down to a limit of detection in the ppb-ppt range21,22,23,24. Unfortunately, AAS and ICP-MS are not realistic means for detection in a traditional biochemistry lab as those methods would require access to specialized equipment and training.
Previous work by Brittain25,26 investigated the use of hydroxynaphthol blue (HNB) as a way to identify the presence of transition metals in solution. However, there were several internal contradictions in the data20 and those works failed to offer an adequate protocol. Studies by Temel et al.27 and Ferreira et al.28 expanded on Brittain&#39;s work with HNB as a potential metal indicator. However, Temel developed a protocol that makes use of AAS for sample analysis, using HNB only as a chelating agent. Ferreira&#39;s study used the change in the HNB absorbance spectra at 563 nm, a region of the free-dye HNB spectra that overlaps heavily with the spectra of HNB-metal complexes at pH 5.7, making the assay sensitivity fairly low as well as resulting in relatively weak metal binding affinity20. To address issues in our own lab with Ni2+ leaching from IMAC, we have expanded the work done by Brittain25,26 and Ferreria28 to develop an easy assay capable of detecting nanomolar levels of several transition metals. We showed that HNB binds nickel and other common for IMAC metals with sub-nanomolar binding affinities and form 1:1 complex over a wide range of pH values20. The assay reported here is based on these findings and utilizes absorbance changes in the HNB spectrum at 647 nm for metal quantification. The assay can be performed in the physiological pH range using common buffers and instrumentation found in a typical biochemistry lab by using colorimetric detection and quantification of metal-dye complexes and the associated change in absorbance of the free-dye when it binds to metal.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2xYT broth</td>
			<td>Fisher Scientific</td>
			<td>BP9743-500</td>
			<td>media for E.coli growth</td>
		</tr>
		<tr>
			<td>HEPES, free acid</td>
			<td>BioBasic</td>
			<td>HB0264</td>
			<td>alternative buffer</td>
		</tr>
		<tr>
			<td>HisPur Ni-NTA resin</td>
			<td>Thermo Scientific</td>
			<td>88222</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydroxynaphthol blue disoidum salt</td>
			<td>Sigma-Aldrich</td>
			<td>219916-5g</td>
			<td></td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>Fisher Scientific</td>
			<td>O3196-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>BioBasic</td>
			<td>IB0277</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS, free acid</td>
			<td>BioBasic</td>
			<td>MB0360</td>
			<td>alternative buffer</td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Fisher Scientific</td>
			<td>S271-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate</td>
			<td>Fisher Scientific</td>
			<td>S369-500</td>
			<td>alternative buffer</td>
		</tr>
		<tr>
			<td>Tricine</td>
			<td>Gold Bio</td>
			<td>T870-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>Fisher Scientific</td>
			<td>BP152-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T9284-500</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantification of metal leaching in immobilized metal affinity chromatography

Contamination of enzymes with metals leached from immobilized metal affinity chromatography (IMAC) columns poses a major concern for enzymologists, as many of the common di-and trivalent cations used in IMAC resins have an inhibitory effect on enzymes. However, the extent of metal leaching and the impact of various eluting and reducing reagents are poorly understood in large part due to the absence of simple and practical transition metal quantification protocols that use equipment typically available in biochemistry labs. To address this problem, we have developed a protocol to quickly quantify the amount of metal contamination in samples prepared using IMAC as a purification step. The method uses hydroxynaphthol blue (HNB) as a colorimetric indicator for metal cation content in a sample solution and UV-Vis spectroscopy as a means to quantify the amount of metal present, into the nanomolar range, based on the change in the HNB spectrum at 647 nm. While metal content in a solution has historically been determined using atomic absorption spectroscopy or inductively coupled plasma techniques, these methods require specialized equipment and training outside the scope of a typical biochemistry laboratory. The method proposed here provides a simple and fast way for biochemists to determine the metal content of samples using existing equipment and knowledge without sacrificing accuracy.

The spectrum of free HNB at neutral pH (black line) and representative spectra of fractions assayed for Ni2+ from the isolation of MSP1E3D129 are shown in Figure 2. A successful assay series should demonstrate a decreased absorbance at 647 nm compared to the HNB control, which corresponds to the formation of HNB complexes in the presence of a transition metal. A failed assay would be indicated by an increase in absorbance at 647 nm. Alternatively, more than...

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Quantification of Metal Leaching in Immobilized Metal Affinity Chromatography

We present an assay for easy quantification of metals introduced to samples prepared using immobilized metal affinity chromatography. The method uses hydroxynaphthol blue as the colorimetric metal indicator and a UV-Vis spectrophotometer as the detector.

Contamination of enzymes with metals leached from immobilized metal affinity chromatography (IMAC) columns poses a major concern for enzymologists, as ...

Our method is significant, as it allows the average biochemist to quickly determine if samples isolated using immobilized metal affinity chromatography are contaminated with transition metals. The main advantage is the ease by which the assay can be performed. The assay uses instrumentation and techniques common to most biochemistry labs, and it can be easily and quickly implemented.While in this article we apply this method for samples isolated with a nickel-NTA column, the method can be used with any other metal affinity resin. First time users should try this method with a nickel stock solution of known concentration. This will familiarize them with the workflow, sample colors, and resins shown in spectral changes.Demonstrating the procedure will be Cole Swain, a technician from my laboratory. To begin, turn on and warm up the UV-Vis spectrophotometer. Determine the chromatography fractions to be assayed using a diode array UV-Vis spectrophotometer with optical absorbance at 280 nanometers to quantify the protein.Obtain 10 to 100 millimolar sample buffer with a PH between 7 and 12, such as Tris, HEPES, MOPS, and phosphate buffer. Prepare a 12%weight by volume solution of HNB dispersion in the sample buffer using 120 milligrams of HNB reagent for each milliliter of stock solution prepared. Set the spectrophotometer to collect data at 647 nanometers.Use a quartz cuvette filled with the sample buffer to blank the spectrophotometer. Prepare a control solution in a cuvette containing 50 microliters of HNB stock per milliliter of total assay volume. Allow the control to incubate for a minimum of three minutes at room temperature.Measure and record the absorbance at 647 nanometers for the control sample. Prepare the assay samples by mixing 150 microliters of HNB stock with 2850 microliters of appropriately diluted protein fractions with the sample buffer. Allow the sample to incubate for a minimum of three minutes at room temperature.Repeat the spectrum recording for each fraction to be measured. In the case where insufficient dilution is obtained, the entire spectral band at 647 nanometers is gone. While with too-strong dilution, the sample is undistinguishable from the control.To determine the concentration of metal in each sample, first find the difference of each sample absorbance at 647 nanometers from the HNB control. Determine the metal concentration in micromolar using the formula where DF is the dilution factor for the assay fraction, delta A-B-S 647 is the absorbance change at 647 nanometers, 3.65 times 10 to the negative 2 represents the extinction coefficient of HNB, and l is cuvette's optical path in centimeters. In this study, the spectrum of free HNB at neutral PH in representative spectra of fractions assayed for nickel ion from the isolation of MSP1E3D1 are shown here.A decreased absorbance at 647 nanometers compared to the HNB control was observed, which corresponded to the formation of HNB complexes in the presence of a transition metal. To demonstrate the application of this assay, two his-tagged membrane scaffold proteins, MSP1E3D1, MSP2N2, and a novel, three-heme, c-type cytochrome GSU0105, from geobacter sulfurreducens, were analyzed. The protein and nickel ion content of each fraction for GSU0105 were significantly shifted from one another, while the fractions for MSP1E3D1 and MSP2N2 that contained the most protein also had the highest nickel content.It is also illustrated that the metal content may not be evenly distributed among fractions collected using a mobilized metal affinity chromatography. It's most important to adequately and consistently mix the blank in all samples and allow for equal incubation times for the blank in all samples. Protein fractions of special interest could be further analyzed with atomic absorption spectrometry or ICPMS to confirm metal contamination and to test for chelated or strongly bound protein metal ions.Besides transition metal leaching detection, this technique can be used to measure binding affinities in transition metal ions to proteins. HNB and any nickel present in samples are irritants to the eyes and skin respectively. Standard PPE including gloves and eye protection should be used during the method.

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7.1K vistas.  James Madison University. Nuestro método es significativo, ya que permite al bioquímico promedio determinar rápidamente si las muestras aisladas mediante cromatografía de afinidad de metales inmovilizadas están contaminadas con metales de transición. La principal ventaja es la facilidad con la que se puede realizar el ensayo. El ensayo utiliza instrumentación y técnicas comunes a la mayoría de los laboratorios de bioquímica, y se puede implementar fácil y rápidamente.Mientras que en este artículo a...