Biosynthesis of intestinal microvillar proteins. Surface expression of aminopeptidase N is not affected by chloroquine

The effect of chloroquine on the biosynthesis of pig intestinal aminopeptidase N (EC 3.4.11.2) was studied by labelling with [35S]methionine in organ cultured mucosal explants. The lysosomotropic agent did not alter the molecular size of either the transient or the mature form of the enzyme and did not markedly influence the relative intracellular distribution of the two forms. The microvillar expression of aminopeptidase N during labelling periods of 80-120 min was found to be unaffected by chloroquine. Together these data indicate that pH neutralization of the acidic compartments of the cell bears no consequence on the intracellular transport of the newly synthesized microvillar enzyme. This suggests that the acidic compartments are not involved in the post-Golgi transport and that this, in turn, probably occurs via a constitutive rather than a regulated pathway.