Perturbation of intestinal microvillar enzyme biosynthesis by amino acid analogs. Evidence that dimerization is required for the transport of aminopeptidase N out of the endoplasmic reticulum.

The amino acid analogs canavanine, 3-hydroxynorvaline, thialysine, 6-fluorotryptophan, m-fluorotyrosine, and 2-fluorophenylalanine were incorporated into proteins, synthesized in pig intestinal mucosal explants, and their effect on molecular processing and intracellular transport of microvillar enzymes studied. Unless they were used in combination, none of the analogs drastically reduced the expression of aminopeptidase N (EC 3.4.11.2) or sucrase-isomaltase (EC 3.2.1.48, EC 3.2.1.10), but to a varying extent, they all slowed the rate of transport to the apical surface. In contrast, the cellular export of a secretory protein, apolipoprotein A-1, was largely unaffected. For the microvillar enzymes, all six analogs caused an accumulation of the transient, high mannose-glycosylated form, indicating an analog-sensitive stage prior to the Golgi-associated processing. For aminopeptidase N, this arrest was shown to correlate with a reduced ability of its transient high mannose-glycosylated form to form homodimers as judged from cross-linking experiments, suggesting dimerization to be obligatory for transport out of the endoplasmic reticulum.