The Occurrence of a Glycine Cleavage System in Mammalian Brain1

A major catabolic route for glycine in liver is its conversion to methylene tetra‐hydrofolate (methylene THF), CO2 and NH3, catalysed by the glycine cleavage system described by Yoshida and Kikuchi (1970). In view of the role of glycine as a putative neuro‐transmitter, the occurrence of this system in mammalian brain was investigated. Our studies demonstrated: (a) that the production of 14CO2 from [1‐14C]glycine required the presence of tetrahydrofolate, NAD, dithiothreitol and pyridoxal phosphate in the reaction mixture; (b) that besides CO2l‐serine was the other major product of the reaction; (c) that glyoxylate did not function as an intermediate in this reaction; and (d) that enzymatic activity appeared to be associated with membranes. All of these properties resembled those previously described for the hepatic system.