A thermochemical investigation of the binding of 12-phosphotungstic acid and chloride ion to bovine serum albumin

Peter W. Carr, Earl B. Smith, Stephen R. Betso, Robert H. Callicott

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Abstract

The reaction of bovine serum albumin (BSA) and several other proteins with 12-phosphotungstic acid (12-PTA) has been investigated by the method of thermometric enthalpy titration. For all proteins tested the enthalpograms indicate that the reaction proceeds in two stages. The reaction of BSA with 12-PTA has been studied as a function of pH From 1 to 5, of ionic strength from 0.10 to 1.0 M in sodium chloride-hydrochloric acid mixtures and as a function of BSA concentration from 0.50 to 20 g I-1. The studies indicate that some chloride (or other anion) binds to or condenses on the surface of the positively charged protein. Other chloride ions are present near the protein only as counter ions in order to satisfy electroneutrality considerations. When I 2-PTA is added slowly and continuously to a protein it first reacts with the available positive sites to which no anion is strongly bound thus: {A figure is presented}. In the second reaction stage the chloride ion is displaced from the protein precipitate by additional 12-PTA. {A figure is presented}.

Original languageEnglish (US)
Pages (from-to)105-121
Number of pages17
JournalThermochimica Acta
Volume15
Issue number1
DOIs
StatePublished - Apr 1976

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