Kinetic properties of glutaminase from cerebral cortex

The rates of phosphate activated glutaminase activity in finely homogenised cerebral cortex and synaptosomes were measured. Activity was 25-50% higher at pH 7.0 than at pH 8.0. Glutamate inhibited activity with a Ki of 2-3 mM while aspartate had little effect. Calcium (1 mM) activated the enzyme but magnesium was without action. The pH profiles of the effects of these modulators of glutaminase activity in these finely ground preparations showed that all agents were more effective at pH 7.0 than at pH 8.0.