[Biosynthesis and post-translational maturation of transferrin in subcellular fractions of rat liver].

Using [14C]leucine pulse label in vivo, the dynamics of transferrin synthesis and its intracellular transport in rat liver and the changes in the molecular sizes of the newly formed transferrin chains during this transport were investigated. The transferrin radioactivity peaks in the rough and smooth endoplasmic reticulum and in Golgi vesicles were observed on the 15th, 20th and 20-30th min after injection of the pulse label. In blood stream the [14C]transferrin was detected 30 min after the label administration, the maximum of radioactivity being observed on the 60th min. The intracellular transport of transferrin was accompanied by changes in its molecular weight. The molecular weights of the transferrin precursors from the rough and smooth endoplasmic reticulum, of immunoreactive transferrin from Golgi vesicles and of circulating transferrin are 86 000-88 000, 84 000 and 77 000, respectively. These variations in molecular weights are indicative of a complex reaction sequence of posttranslational maturation of transferrin in the liver, which includes in all probability proteolysis and glycosylation.