Bestatin transport in rabbit intestinal brush-border membrane vesicles.

The effect of papain treatment on bestatin uptake by rabbit intestinal brush-border membrane vesicles (BBMVs) was studied. Papain treatment of BBMVs effectively diminished aminopeptidase activity but not bestatin uptake by a H+/dipeptide cotransporter. Bestatin uptake by BBMVs was composed of two saturable components, and after papain treatment the high-affinity component disappeared while the low-affinity component was retained. These findings suggest that high- and low-affinity components represent bestatin binding to aminopeptidase and the true uptake by the H+/dipeptide cotransporter, respectively.