Electrostatic Control Of Enzyme Reactions: The Mechanism Of Inhibition Of Glucose Oxidase By Putrescine

Document Type

Article

Publication Date

8-15-1984

Published In

Archives Of Biochemistry And Biophysics

Abstract

The interaction of putrescine dihydrochloride with glucose oxidase is reported. At pH 7.65 glucose oxidase is strongly anionic (Z = −80). The pKₐ of an essential acidic group on the reduced form of the enzyme is extremely sensitive to ionic strength, as predicted by simple electrostatic theory [J. G. Voet, J. Coe, J. Epstein, V. Matossian, and T. Shipley (1981), Biochemistry, 20, 7182–7185]. Putrescine dihydrochloride was found to inhibit glucose oxidase at pH 7.65 at a constant ionic strength of 0.05. The kinetics do not obey simple competitive inhibition, however. The data can best be explained by a model in which change in the electrostatic potential of the enzyme on putrescine binding changes the observed pKₐ of the essential acidic group. The pH dependence of putrescine inhibition supports this interpretation. At I = 0.05, 5 mM putrescine was found to change the pKₐ of the essential acidic group from 7.6 to 7.1. The shift in the pKₐ as a function of putrescine concentration at pH 7.7 and I = 0.05 also supports the model presented. The Kₐ for putrescine to the active form of the enzyme was calculated to be 4.2 mm.

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