Mechanisms of Inhibition and Activation of Beef Liver D-Glycerate Dehydrogenase by Inorganic Anions

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Abstract
Fluorescence titration of beef liver D-glycerate dehydrogenase [EC 1. 1. 1. 29] provided evidence for the presence of two substrate binding sites (S and S′ sites) on the enzyme protein. Kinetic studies indicated that inhibition of the enzyme by inorganic anions resulted from competition of the anions with the substrate at the S site. It was also shown that the binding of hydroxypyruvate to the S′ site was responsible for the substrate inhibition, and that inorganic anions, when bound to the S′ site, activated the enzyme. These findings explained the release by addition of inorganic anions of the substrate inhibition in the presence of high concentrations of hydroxypyruvate. When the activity was plotted against the anion concentrations, a sigmoid curve was obtained. An analysis of this sigmoid curve demonstrated that the enzyme possessed at least three anion binding sites, one of which being the S′ site. Based on these findings, a hypothetical model is presented for the mechanisms of inhibition and activation of the enzyme by inorganic anions.

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