Related Experiment Videos
Ontogeny of membrane and soluble amino-oligopeptidases in rat intestine
A M Reisenauer1, E A Lee, R O Castillo
1Department of Pediatrics, Stanford University, California 94305.
Insights
Intestinal amino-oligopeptidase (AOP) activity changes during rat development. Membrane AOP activity increases, while soluble AOP decreases, suggesting the membrane form may be a precursor.
Area of Science:
- Biochemistry
- Molecular Biology
- Gastroenterology
Background:
- Intestinal amino-oligopeptidase (AOP) is crucial for protein digestion.
- Understanding AOP's developmental changes is key to comprehending nutrient absorption.
- Postnatal development involves significant physiological adaptations in the gastrointestinal tract.
Purpose of the Study:
- To characterize the postnatal development of intestinal amino-oligopeptidase (AOP).
- To compare the structures and biochemical properties of membrane-bound and soluble AOP.
- To investigate the relationship between membrane and soluble AOP forms.
Main Methods:
- Measurement of AOP activity in intestinal membrane and cytosolic fractions of suckling and weaned rats.
- Comparison of subunit structures and biochemical characteristics (substrate affinity, pH optima, inhibition, antigenicity) of membrane and soluble AOP.
- Analysis of N-linked glycosylation and protein precursor-relationship using radiolabeling ([35S]methionine incorporation).
Main Results:
- Jejunal membrane AOP activity doubled at weaning, while ileal soluble AOP activity decreased abruptly.
- Maturation of ileal membrane AOP involved changes in N-linked glycosylation, increasing its molecular mass.
- Membrane and soluble AOP shared similar biochemical properties, but soluble AOP was smaller (25-35 kDa less).
- radiolabeling indicated membrane AOP is a precursor to soluble AOP.
Conclusions:
- Membrane and soluble AOP are related proteins with distinct developmental patterns.
- Soluble AOP may originate from the endocytosis of membrane-bound AOP.
- These findings shed light on the dynamic regulation of digestive enzyme activity during development.
Abstract:
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.