A microenvironmental redox shift at a charged surface detected by papain activity
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The relative activity of an SH-enzyme, papain, is decreased by increasing the mole ratio of oxidizing disulfide to reducing thiol in solution. The same inverse relationship applies to papain adsorbed on charged clay particles, but electrostatic interactions among the charged particles and charged disulfides and thiols significantly shift the dependence. Papain activity thus reflects the microenvironmental redox potential in the vicinity of the charged particles. The redox pairs cystine dimethylester-cysteine ethylester, dithiodiglycolic acidmercaptoacetic acid, and dithiodiglycol-mercaptoethanol were used in the assays. A special form of the Boltzmann distribution must be used to calculate mole ratios of ions of different charge near a charged interface.
KeywordsDisulfide Thiol Kaolinite Papain Charged Interface
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