title: Biosynthesis of intestinal microvillar proteins. The intracellular transport of aminopeptidase N and sucrase-isomaltase occurs at different rates pre-Golgi but at the same rate post-Golgi.
abstract: The kinetics of processing and microvillar expression of aminopeptidase N (EC 3.4.11.2) and sucrose alpha-D-glucohydrolase-oligo-1,6-glucosidase (sucrase-isomaltase, EC 3.2.1.48 and EC 3.2.1.10) were compared by labelling of pig small intestinal mucosal explants with [35S]methionine. The conversion from transient (high mannose glycosylated) to mature (complex glycosylated) form was 1.7-times slower for sucrase-isomaltase than for aminopeptidase N, indicating a slower rate of migration from the rough endoplasmic reticulum to the Golgi complex. Likewise, sucrase-isomaltase appeared in the microvillar fraction at a slower rate than aminopeptidase N. The relative pool sizes of mature and transient forms of both enzymes in intracellular membranes (Mg2+-precipitated fraction) were determined to obtain information on the relative time, spent pre- and post-Golgi, respectively, prior to microvillar expression. This ratio was 0.24 +/- 0.06 (mean +/- SD) for sucrase-isomaltase as compared to 0.40 +/- 0.04 (mean +/- SD) for aminopeptidase N. Considering the slower rate of pre-Golgi transport for sucrase-isomaltase, this indicates that the two microvillar enzymes have rather similar if not identical rates of post-Golgi transport.
authors.forename: E M
authors.initials: EM
authors.lastname: Danielsen
authors.forename: G M
authors.initials: GM
authors.lastname: Cowell
mesh_terms: D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D018826:CD13 Antigens; D006056:Golgi Apparatus / Q000201:enzymology*; D007413:Intestinal Mucosa / Q000201:enzymology*; D007421:Intestine, Small / Q000201:enzymology; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D009924:Organ Culture Techniques; D014176:Protein Biosynthesis; D013394:Sucrase-Isomaltase Complex / Q000378:metabolism*; D013552:Swine
chemical_list: D009097:Multienzyme Complexes; D013394:Sucrase-Isomaltase Complex; D000626:Aminopeptidases; D018826:CD13 Antigens