Assessment of protein turnover in perfused rat liver. Evidence for amino acid compartmentation from differential labeling of free and tRNA-gound valine.

作者：Edward A. Khairallah, Glenn E. Mortimore · 发表于：Journal of Biological Chemistry · 年份：1976 · DOI：10.1016/s0021-9258(17)33750-x · 被引用次数：192 · 研究领域：Muscle metabolism and nutrition、Liver Disease Diagnosis and Treatment、Biochemical effects in animals

Total protein synthesis in perfused livers of fed rats was determined by measuring the rate of valine incorporation based on the specific activity of valine attached to tRNA. Rates were not significantly altered when perfusate valine was increased from 0.40 to 5 mM and were similar to values calculated earlier from the specific activity of extracellular valine at a concentration of 15 mM. Overall protein degradation, computed from the sum of the rates of synthesis and the total increase of free intra- and extracellular valine, corresponded closely to the increase of free valine that occurred between 5 and 15 min after the addition of cycloheximide. In the latter experiments advantage was taken of the fact that the previously established suppressive effect of cycloheximide on proteolysis does not begin initially with the inhibition of synthesis, but 15 min later. Thus, the release of valine from 5 to 15 min was assumed to represent rates of protein degradation in effect prior to the addition of cycloheximide. The close agreement found among these independent assessments of protein metabolism thus appears to eliminate much of the previous uncertainty in the quantitation of hepatic protein turnover. In the course of these studies we noted that the specific activity of valyl-tRNA attained steady state values that were intermediate between specific activities of the extracellular and intracellular pools, but appeared to reach a steady state sooner than that of intracellular valine...