Reactivation of substrate-inactivated brain glutamate decarboxylase

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Abstract
The effects of ATP and inorganic phosphate (Pi) on the reactivation of glutamate apodecarboxylase by its cofactor pyridoxal-5′-phosphate (pyridoxal-P) was studied. Apoenzyme was prepared by preincubation with glutamate. Apoenzyme prepared with glutamate alone was reactivated slowly and incompletely by adding a saturating concentration of pyridoxal-P (20µM). Reactivation was slightly enhanced by 1–10 mM Pi. Reactivation by pyridoxal-P plus Pi was greatly enhanced by the presence of low concentrations (100µM), possibly by competition of ATP for the cofactor binding site. Four factors (glutamate, pyridoxal-P, ATP, and Pi) control a cycle of inactivation and reactivation that appears to be important in the regulation of brain glutamate decarboxylase.