Evidence for selective transport of two brush-border glycoproteins from endoplasmic reticulum to Golgi complex in rabbit enterocytes.

In vivo pulse-chase labeling of rabbit jejunum loops was used in conjunction with subcellular fractionation and quantitative immunoprecipitation to compare the intracellular transport kinetics of aminopeptidase with that of a 140 kDa brush-border antigen not belonging to the hydrolase class. As judged by the maturation kinetics of Asn-linked glycans, these glycoproteins were found to be transported from the endoplasmic reticulum into the Golgi apparatus at different rates (t1/2 = 25-50 min). The transport from the Golgi complex to the brush-border was rapid and seemed to occur at the same rate for both glycoproteins. In keeping with these kinetic data, the steady-state levels of aminopeptidase and the 140 kDa antigen in the Golgi complex were low, although that of aminopeptidase was significantly higher.