Document Detail


Determination of interactive thiol ionizations in bovine serum albumin, glutathione, and other thiols by potentiometric difference titration.
MedLine Citation:
PMID:  7008829     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
A potentiometric difference titration (PDT) method is used to study the ionization behavior of the thiol group in bovine serum albumin and in the following less complex compounds: glutathione, cysteine, 2-mercaptoethanol, 3-mercaptopropionic acid, 2-mercaptoethylamine, cis-2-mercaptocyclobutylamine, 2-aminothiophenol, and 5-mercapto-2-nitrobenzoic acid. In the PDT method the pH dependence of the amount of protons released in the reaction RSH + CH3SO2SCH3 leads to RSSCH3 + CH3SO2- + H+ is measured in order to obtain the pH dependence of the molar proton content of the thiol (hu) relative to the molar proton content of its methylthio derivative (hm). The pH dependence of hu--hm reflects the ionization behavior of the thiol group and of other groups whose ionization is thermodynamically linked to that of the thiol group. Data presented here indicate that the ionization behavior of the single thiol group in albumin is strikingly different in the native and the urea-denatured proteins. Three ionizable groups appear to affect ionization of the thiol in the native protein whereas only one group appears to affect ionization of the thiol in the urea-denatured protein. Furthermore, the measured PDT curves are consistent with an abnormally high acidity (pK less than 5) for the thiol in native albumin and a normal acidity for the thiol in the urea-denatured protein. Comparisons of microscopic ionization constants determined for cysteine by using the PDT method with those determined by other methods indicate that the PDT method should be useful in characterizing the ionization behavior of thiol groups in proteins and other polyprotic substances.
Authors:
S D Lewis; D C Misra; J A Shafer
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  19     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1980 Dec 
Date Detail:
Created Date:  1981-05-21     Completed Date:  1981-05-21     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  6129-37     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Animals
Cattle
Chemical Phenomena
Chemistry
Glutathione / analysis*
Hydrogen-Ion Concentration
Indicator Dilution Techniques
Methyl Methanesulfonate / analogs & derivatives
Potentiometry
Serum Albumin, Bovine / analysis*
Sulfhydryl Compounds / analysis*
Grant Support
ID/Acronym/Agency:
AM-09276/AM/NIADDK NIH HHS
Chemical
Reg. No./Substance:
0/Serum Albumin, Bovine; 0/Sulfhydryl Compounds; 2949-92-0/methyl methanethiosulfonate; 66-27-3/Methyl Methanesulfonate; 70-18-8/Glutathione

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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