Subcellular localization in normal and vitamin A-deficient rat liver of vitamin A serum transport proteins,albumin, ceruloplasmin and class I major histocompatibility antigens

The subcellular localization in rat liver cells of retinol-binding protein (RBP), prealbumin, ceruloplasmin, albumin, and class I transplantation antigen chains was investigated by radioimmunoassay determinations. The concentration of RBP was high in the rough and smooth endoplasmic reticulum (SER). The relative concentrations of prealbumin, ceruloplasmin and albumin were similar in the endoplasmic reticulum fractions and in the Golgi fraction. Neither of the proteins were found in significant amounts in the post-microsomal supernatant nor in the plasma membrane. The concentrations of the class I transplantation antigen chains were higher in the Golgi fraction than in the endoplasmic reticulum fractions. In the rough endoplasmic reticulum (RER) fraction ceruloplasmin and the class I antigens partially interact with high-molecular weight (MW) components, presumably membrane-bound glycosyltransferases. RBP, prealbumin and albumin seemed to be present in free form within the microsomal lumen. In vitamin A deficiency the RBP and to a lesser extent the prealbumin concentrations in the endoplasmic reticulum fractions were significantly increased, as compared to fractions from normal livers. This suggests that the presence of vitamin A is a prerequisite for the transport of RBP from the endoplasmic reticulum to the Golgi complex. The intracellular concentrations of albumin and ceruloplasmin were not significantly altered by vitamin A deficiency. In contrast, the amounts of the class I antigen heavy chains were found to be increased.