AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 1 178-G184, Copyright © 1992 by American Physiological Society
Ontogeny of membrane and soluble amino-oligopeptidases in rat intestine
A. M. Reisenauer, E. A. Lee and R. O. Castillo
Department of Pediatrics, Stanford University, California 94305.
Intestinal amino-oligopeptidase (AOP) plays an essential role in protein
digestion. To characterize its postnatal development, we measured AOP
activity in intestinal membrane and cytosolic fractions in suckling and
weaned rats, compared the subunit structures of the membrane and soluble
enzymes, and assessed the biochemical relationship of these peptidases. At
weaning, jejunal membrane AOP activity doubled while soluble AOP activity
in the ileum fell abruptly. The maturational increase in the molecular mass
of ileal membrane AOP was due to alterations in the N-linked glycosylation
of this protein. Ileal membrane and soluble AOP exhibited similar substrate
affinities, pH optima, inhibition characteristics, and antigenic epitopes.
However, soluble AOP was 25-35 kDa smaller than the membrane enzyme. Peak
incorporation of [35S]methionine into ileal brush-border AOP preceded
maximal radioactivity in soluble AOP, suggesting that the membrane
peptidase is a precursor of the soluble enzyme. We conclude that membrane
and soluble AOP are closely related proteins with distinct developmental
profiles and that the soluble peptidase may be derived from endocytosis of
the membrane enzyme.
