Studies on the biosynthesis of albumin and proteins in human liver tissue

Abstract

Abstract. The incorporation rate of leucine into albumin and the incorporation rate of leucine into hepatic proteins were determined in human liver tissue slices.Leucine was linearly incorporated into hepatic tissue albumin, into albumin released into the incubation medium, and into hepatic proteins during 4 h incubation. Amino acids stimulated the albumin and hepatic protein synthesis in vitro and in vivo. The incorporation rate of leucine into hepatic albumin and tissue proteins was correlated to hepatic RNA concentration.In twenty‐one experiments the mean incorporation rate of leucine into hepatic tissue immunoreactive albumin was 5.1±0.6 μmol leucine h‐1 g albumin‐1 (mean±; SEM), and 0.87±;0.17 μmol leucine h‐1 g albumin‐1 into albumin released to the incubation medium. By crossed immunoelectrophoresis, the hepatic immunoreactive albumin could be partly resolved into two components one of which migrated at the same rate and the other at a lower rate than serum albumin. Treatment of the slowly migrating component with a low concentration of trypsin changed its mobility to that of serum albumin. Gel filtration through Sephadex G‐100 of the slowly migrating fraction showed that it had similar molecular size as that of serum albumin. The results support the hypothesis that human hepatic albumin biosynthesis involves a polypeptide precursor similar to that described for the rat liver.