Protein synthesis with special reference to S-100 protein in brain slices from rats receiving a restricted protein supply.

The synthesis of S-100 protein and that of soluble and total proteins was investigated using cerebral slices from rats fed a 20% or 3% protein containing diet for 6 days. Incorporation of radioactive amino acids into S-100 protein was significantly higher when rats were fed a diet containing 20% protein. No significant differences were obtained in the radioactivity incorporated into total or soluble proteins between the 2 dietary groups. 14C-leucine of aspecific radioactivity of 55 mCi/mmol or 3.2 mCi/mmol incorporated with time into total protein was similar for the 2 dietary groups. The time-dependent uptake of 14C-leucine by the slices and theinulin space remained unaffected by the dietary conditions used; and amino acid analyser estimates of the free amino acid pool showed no significant differences. Brain wet weight was 1.54+/-0.02 g and1.39+/-0.02 g for protein-fed and protein-restricted rats respectively. The corresponding body weight increased by 7.8 g/day or fell by 0.5 g/day. Although the differences observed in total protein synthesis were small the synthesis of a nervous tissue specific protein S-100 was markedly affected by short-term protein restriction.