Interconversion of glycine and serine in a synaptosome fraction isolated from the spinal cord, medulla oblongata, telencephalon, and cerebellum of the rat.

Abstract

AbstractThe metabolism of glycine was studied in vitro using preparations of synaptosomes (P2) isolated from the spinal cord, medulla oblongata, telencephalon, and cerebellum of the rat. The content of aspartate, glutamate, glutamine, serine, threonine, glycine, and alanine was determined in the crude synaptosomal fraction (P2) from the four regions of the CNS. In general, the content of the amino acids in the subcellular fraction from the medulla oblongata and spinal cord resembled one another whereas the same was true for the telencephalon and cerebellum. Significantly greater amounts of glutamate, aspartate, glutamine, and serine were found in the synaptosomal fraction of the telencephalon and cerebellum than in similar P2 fractions from the medulla oblongata and spinal cord. On the other hand, glycine had a higher content in the latter two preparations than in the P2 fractions from the telencephalon and cerebellum. [U‐14C]‐serine and [U‐14C]‐glycine were readily taken up by the crude synaptosomal fractions. The rate of conversion of serine to glycine appeared to be 18.5, 3.9, 2.9, and 2.7 times greater than the conversion of glycine to serine in the incubated synaptosomal fractions from the cerebellum, spinal cord, medulla oblongata, and telencephalon, respectively. The conversion of serine carbons into glycine appeared to be 2.5, 1.9 and 1.6 times greater in the synaptosomal fraction from the cerebellum, spinal cord, and medulla oblongata than in similar preparations from the telencephalon. The data are discussed in terms of the possible synthesis pathway for the pool of glycine used as a transmitter.