REGIONAL DISTRIBUTION AND PROPERTIES OF THE GLYCINE CLEAVAGE SYSTEM WITHIN THE CENTRAL NERVOUS SYSTEM OF THE RAT: EVIDENCE FOR AN ENDOGENOUS INHIBITOR DURING IN VITRO ASSAY

—The activity of the glycine cleavage system (GCS) was determined in homogenates from five specific regions of the rat CNS (telencephalon, midbrain, cerebellum, medulla‐pons, and spinal cord). An inverse trend was noted between the glycine content and the specific activity of the GCS in the regions. A 25‐fold range in the enzyme activities was found between the telencephalon (highest) and the spinal cord (lowest). The properties of the GCS activity in CNS homogenates agreed with those properties previously described for this system in partially purified preparations of liver and brain mitochondria (Kikuchi, 1973; Bruinet al., 1973). Within the CNS homogenates, the liberation of CO2 from the carboxyl carbon of glycine was quantitatively coupled to the formation of serine.