engleski

Kinetic properties of alkaline phosphatases

The active site accessibility and substrate specificity of the bacterial and mammalian alkaline phosphatases have been investigated using a variety of structurally related alternative substrates, i.e. dialkyl substituted phenyl phosphates. Although large aliphatic side chains do have some influence on substrate binding, the absence of a major steric effect suggests considerable freedom of the leaving group in the ES complex of the human alkaline phosphatases. E.coli alkaline phosphatase exibits restricted binding affinity, indicating speciffic structural differences between the bacterial and the mammalian enzymes. Introduction of an alternative substrate into the reaction system permitted further analysis of the reaction mechanism. The observed deviations from Michaelis-Menten kinetics were investigated in terms of negative cooperative interactions or enzyme asymmetry. Data obtained by non-linear regression curve fitting tend to suggest a mechanism based on independent nonequivalent subunits rather than negative cooperative interactions between subunits of a dimeric enzyme.

alkaline phosphatases ; dialkyl substituted phenyl phosphates ; selective inhibition ; asymmetry, curve fitting

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