PROTEIN SYNTHESIS IN NEURONAL PERIKARYA ISOLATED FROM CEREBRAL CORTEX OF THE IMMATURE RAT 1

Abstract

Homogenates of neuronal perikarya isolated from the cerebral cortex of the 8-day-old rat were incubated with [ 3 H]leucine, and the characteristics of the protein synthetic process were studied. Incorporation of leucine into protein was linear up to 90 min, proceeded optimally at pH 7.6 and was stimulated by K + and NH 4 + , unaffected by Li + and inhibited by Na + . Puromycin, cycloheximide, RNAse, sulphhydryl blocking agents and phospholipase A exerted a pronounced inhibition, whereas chloramphenicol and phospholipase C had no effect. About 42 per cent of the total radioactive protein formed in the optimally fortified in uitro system was recovered in non-sedimentable form. Incorporation into the subcellular fractions of the neuronal perikarya increased steadily with increasing time of incubation. The microsomal fraction acquired the highest specific radioactivity (d.p.m./mg of protein), followed by the mitochondrial and the nuclear + cell debris fractions. The high-speed soluble fraction exhibited the lowest specific radioactivity. Although the addition of L-methionine to a suitably fortified incubation medium inhibited neuronal protein synthesis by about 80 per cent, the addition of D-methionhe, Α-methyl-DL-methionine or L-tryptophan was relatively ineffective by comparison.