Biosynthesis of intestinal microvillar proteins. Characterization of intestinal explants in organ culture and evidence for the existence of pro-forms of the microvillar enzymes.
Explants of pig small intestine were maintained at 37 degrees C in organ culture for periods up to 24 h in a system using Trowell T-8 medium supplemented with 10% foetal-calf serum. The mucosal morphology was well preserved during culture, as judged by light and electron microscopy. The explant contents of protein and two brush-border enzymes, microvillus aminopeptidase (EC 3.4.11.2) and dipeptidyl peptidase IV (EC 3.4.14.5), were not significantly modified during culture compared with controls, but a moderate, continuous release of both protein and enzyme activities into the medium was observed. Continuous labelling with [35S]methionine resulted in an even incorporation of radioactivity in the protein components, and the rate of labelling only moderately decreased over the 24 h period. The polypeptide compositions of sucrase (EC 3.2.1.48)--isomaltase (EC 3.2.1.10), maltase--glucoamylase (EC 3.2.1.20) lactase (EC 3.2.1.23)--phlorizin hydrolase (EC 3.2.1.62), microvillus aminopeptidase and aspartate aminopeptidase (EC 3.4.11.7) synthesized during culture were studied, and some were found to be similar to those of the pro-forms of the enzymes isolated from animals that had had their pancreatic duct disconnected 3 days before being killed. These results confirmed earlier findings of the existence of pro-forms of some of the microvillar enzymes and thus indicate a low activity of pancreatic proteinases in the culture system.
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000378:metabolism; D007123:Immunoelectrophoresis, Two-Dimensional; D007421:Intestine, Small / Q000201:enzymology* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000096:biosynthesis*; D008871:Microvilli / Q000201:enzymology; D009924:Organ Culture Techniques; D010455:Peptides / Q000032:analysis; D013552:Swine
D004792:Enzyme Precursors; D008565:Membrane Proteins; D010455:Peptides