Changes in some properties of glutamate decarboxylase activity during the maturation of the brain.

The sensitivity of cerebral glutamate decarboxylase (GAD) activity to hypotonic homogenization medium, centrifugation, Triton-X-100, and preincubation at 37°C was studied in the developing mouse. In newborn and 5-day-old animals, GAD activity was markedly inhibited by all these conditions. From 5 days to adult age, the sensitivity of the enzyme to the experimental conditions used decreased progressively, with the greatest change between the 10th and 15th days. It is concluded that the newborn form of the enzyme, which is unstable and shows a relatively high affinity for pyridoxal phosphate, is substituted by the adult form during the maturation of the brain. The activity of the adult form is much more stable and more dependent on free pyridoxal phosphate. The implications of these findings in the regulation of cerebral excitability during development are discussed.