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Biosynthesis of intestinal microvillar proteins
Author(s) -
Danielsen E.Michael,
Cowell Gillian M.
Publication year - 1984
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(84)80038-1
Subject(s) - tunicamycin , sucrase , biochemistry , enterocyte , glycosylation , maltase , mannose , enzyme , leupeptin , cycloheximide , methionine , biology , chemistry , small intestine , protein biosynthesis , amino acid , protease , endoplasmic reticulum , unfolded protein response
The effect of tunicamycin on synthesis and intracellular transport of pig small intestinal aminopeptidase N (EC 3.4.11.2), sucrase‐isomaltase (EC 3.2.1.48–10) and maltase‐glucoamylase (EC 3.2.1.20) was studied by labelling of mucosal explants with [ 35 S]methionine. The expression of the microvillar enzymes was greatly reduced by tunicamycin but could be partially restored by leupeptin, suggesting the existence of a mechanism whereby newly synthesized, malprocessed enzymes are recognized and degraded. In the presence of tunicamycin, polypeptides likely to represent non‐glycosylated forms of the enzymes persisted in the Mg 2+ ‐precipitated membrane fraction, indicating that high mannose glycosylation is essential for transport to the microvillar membrane. Treatment of aminopeptidase N and sucrase‐isomaltase with endo F reduced the size of the high mannose forms approximately to those seen in the presence of tunicamycin. The complex forms were also sensitive to endo F but did not coincide with the high mannose forms after treatment, indicating that the size difference cannot alone be ascribed to processing of N‐linked carbohydrate.