Amino acid supply and protein metabolism in Ehrlich ascites tumour cells. 2. Incorporation of 14C-tyrosine.

The incorporation of 14C-tyrosine into protein of incubated Ehrlich ascites tumour cells was measured over a 10-fold range of external amino acid concentrations, the composition of which simulated that of mouse intraperitoneal fluid. Incorporation was linear with time and the rate of incorporation increased with increasing external amino acid concentration up to at least six times intraperitoneal concentrations. Further increases in external amino acid supply did not yield a concomitant increase in the rate of tyrosine incorporation, a maximum fractional protein synthetic rate of approximately 100% d-1 being achieved. The specific activity of tyrosine in intracellular fluid was approximately 95% of that of extracellular fluid, irrespective of the external amino acid concentration.