Preferential utilization of exogenously supplied leucine for protein synthesis in estradiol-induced and uninduced cockerel liver explants.
A cockerel liver explant system has been used to study protein synthesis and ribosome transit times. After a 2-hr preincubation of explant tissue in the presence of a large concentration of nonradioactive leucine, a small quantity of [3H]leucine was added and the kinetics of uptake of [3H]leucine into the intracellular acid-soluble leucine pool was compared to the incorporation of [3H]leucine into protein. Incorporation of [3H]leucine into protein reaches a linear rate almost immediately after addition of label, whereas the acid-soluble pool does not reach constant specific activity until much later. The length of time needed to reach a linear rate of incorporation of [3H]leucine into protein is approximately equal to the length of time needed to equilibrate nascent polypeptide chains with labeled precursor--that is, one average ribosome transit time. Therefore, it seems that the immediate precursor pool for protein synthesis reaches constant specific activity almost instantly after addition of [3H]leucine. The results indicate that at least part of the supply of leucine for protein synthesis is derived directly from the exogenous incubation medium and not from the intracellular acid-soluble amino acid pool.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002645:Chickens; D004958:Estradiol / Q000494:pharmacology*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009924:Organ Culture Techniques; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism
D000596:Amino Acids; D011506:Proteins; D004958:Estradiol; D007930:Leucine