Distribution of Serine Hydroxymethyltransferase and Glycine Transaminase in Several Areas of the Central Nervous System of the Rat

Abstract —The regional distributions of serine hydroxymethyltransferase (SHMT) and glycine transaminase (GT) have been determined in five areas of the CNS of the rat. The SHMT activity per mg protein varied in these areas in the following order: medulia‐pons and spinal cord > cerebellum > midbrain > telencephalon. The GT activity per mg protein was essentially the same in the four brain areas, whereas, in the spinal cord it was lower. The activity of GT did not correlate with the glycine content ( r =−0.45. P > 0.05). However, SHMT activity per mg protein was correlated with the glycine content in four regions (the telencephalon, midbrain, medulla‐pons and spinal cord; r = 0.997, P < 0.05). When the activity of SHMT was expressed per relative number of mitochondria, the enzyme levels were correlated with the glycine content in all five areas ( r = 0.952, P < 0.05). The distribution of SHMT was determined in the primary subcellular fractions of the CNS. The SHMT activity in these areas of the CNS appeared to be located predominately in paniculate structures, while only 1 to 4 per cent was found in the soluble fraction. The crude nuclear (P 1 ) and the crude mitochondrial (P 2 ) fractions contained 90–97 per cent of the activity. Subfractionation of P 2 pellets obtained from the telencephalon, medulla‐pons and spinal cord indicated the SHMT activity was localized in both ‘free’ and occluded mitochondria.