PROTEIN SYNTHESIS IN THE PERFUSED RAT LIVER

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Abstract
When rat livers were perfused with whole rat blood (200 ml) containing either 76.7 u moles of added lysine-C14 or histidine-C14 the specific activity of the amino acid immediately fell due to admixture with the preformed amino acid in the system. During the following 4 hours, there was a further fall to 25-35% of the value seen after mixing. In the same system the labeled amino acids were incorporated into protein which appears in the per-fusion fluid. When the apparent incorporations were calculated, using the initial specific activity of the added lysine, in one experiment the incorporation in 4 hours amounted to 1.16 [mu]moles/ g of protein but when the value was corrected for the dilution a value of 7.35 was found. Moreover, the apparent fall in rate of incorporation with time which was observed in experiments with the amino acids mentioned and also with methionine S35, was due primarily to the change in specific activity of the precursor. It was not due to lack of substrate. Those experiments reempha-size the importance of measuring the specific activity of precursors.