The Biosynthesis of Rat Serum Albumin

Abstract

Abstract The role of the Golgi apparatus in the secretion of serum albumin has been investigated by measurements on albumin isolated immunologically from rough microsomes, smooth microsomes, and Golgi-rich fractions prepared from rat liver. Albumin constituted 6% of the total protein of the Golgi-rich fraction, which was the highest level found among intracellular components. After intravenous injection of 14C-leucine the maximum radioactivity of albumin occurred at about 5 min in rough microsomes, 15 min in smooth microsomes, and 20 min in the Golgi-rich fractions. The results indicate the pathway of albumin secretion to be: rough membranes-smooth membranes-Golgi bodies-blood. On the basis of relative specific radioactivities rough and smooth membrane fractions may contain some albumin not normally in the process of active synthesis and secretion, which could represent albumin in temporarily quiescent membrane channels or in pinocytotic vesicles.