EFFECT OF NONPROTEIN THIOLS ON PROTEIN-SYNTHESIS IN ISOLATED RAT HEPATOCYTES

The ability of nonprotein thiols to modulate rates of protein synthesi s was investigated in isolated rat hepatocytes. Addition bf cysteine s timulates protein labelling by [C-14]Leucine. Glutathione depletion, i nduced by in vivo administration of L-buthionine sulfoximine and dieth ylmaleate, did not alter the effect of cysteine, although it decreased the rate of protein synthesis by 32%. The effect of cysteine on prote in synthesis does not seem to be related to a perturbation of the redo x state of the NAD(+)/NADH system or to changes in the rate of glucone ogenic pathway. The following observations indicate that cysteine may stimulate protein synthesis by increasing intracellular levels of aspa rtate: 1. Amino-oxyacetate, an inhibitor of pyridoxal-dependent enzyme s, inhibits protein labelling and decreases aspartate cellular content , whereas most amino acids accumulate or remain unchanged; 2. Cysteine , in the absence or in the presence of amino-oxyacetate, stimulates pr otein labelling and induces aspartate accumulation, although most amin o acids diminish or remain unchanged.