Biosynthesis of intestinal microvillar proteins. Pulse-chase labelling studies on maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV.
The biogenesis of three intestinal microvillar enzymes, maltase-glucoamylase (EC 3.2.1.20), aminopeptidase A (aspartate aminopeptidase, EC 3.4.11.7) and dipeptidyl peptidase IV (EC 3.4.14.5), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. The earliest detectable forms of the enzymes were polypeptides of Mr 225000, 140000 and 115000 respectively. These were found to represent the enzymes in a 'high-mannose' state of glycosylation, as judged by their susceptibility to treatment with endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96). After about 40-60 min of chase, maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV were further modified to yield the mature polypeptides of Mr 245000, 170000 and 137000 respectively, which were expressed at the microvillar membrane after 60-90 min of chase. The fact that the enzymes before reaching the microvillar membrane were found in a Ca2+-precipitated membrane fraction (intracellular and basolateral membranes), but not in soluble form, indicates that during biogenesis maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV are transported and assembled in a membrane-bound state.
D000118:Acetylglucosaminidase / Q000494:pharmacology; D000626:Aminopeptidases / Q000096:biosynthesis*; D000818:Animals; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000096:biosynthesis*; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000096:biosynthesis*; D005087:Glucan 1,4-alpha-Glucosidase / Q000096:biosynthesis*; D005959:Glucosidases / Q000096:biosynthesis*; D043384:Glutamyl Aminopeptidase; D007421:Intestine, Small / Q000187:drug effects / Q000201:enzymology*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008565:Membrane Proteins / Q000096:biosynthesis*; D008871:Microvilli / Q000187:drug effects / Q000201:enzymology; D009924:Organ Culture Techniques; D013552:Swine
D008565:Membrane Proteins; D005959:Glucosidases; D005087:Glucan 1,4-alpha-Glucosidase; D000118:Acetylglucosaminidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D010450:Endopeptidases; D000626:Aminopeptidases; D043384:Glutamyl Aminopeptidase; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases