title: Evidence for biosynthesis of lactase-phlorizin hydrolase as a single-chain high-molecular weight precursor.
abstract: Precursor forms of lactase-phlorizin hydrolase, sucrase-isomaltase and aminopeptidase N were studied by pulse-labelling of organ-cultured human intestinal biopsies. After labelling the biopsies were fractionated by the Ca2+-precipitation method and the enzymes isolated by immunoprecipitation. The results indicate that the lactase-phlorizin hydrolase is synthesized as a Mr 245 000 polypeptide, which is intracellularly cleaved into its mature Mr 160 000 form. Sucrase-isomaltase is shown to be synthesized as a single chain precursor (Mr 245 000 and 265 000) while the precursor of aminopeptidase N is shown to be of apparently the same size as the mature enzyme (Mr 140 000 and 160 000).
mesh_terms: D000626:Aminopeptidases / Q000096:biosynthesis / Q000302:isolation & purification; D018826:CD13 Antigens; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000096:biosynthesis*; D005959:Glucosidases / Q000096:biosynthesis*; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology*; D010694:Lactase-Phlorizin Hydrolase / Q000096:biosynthesis* / Q000302:isolation & purification; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000096:biosynthesis* / Q000302:isolation & purification; D009924:Organ Culture Techniques; D013394:Sucrase-Isomaltase Complex / Q000096:biosynthesis / Q000302:isolation & purification; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000302:isolation & purification
chemical_list: D004792:Enzyme Precursors; D009097:Multienzyme Complexes; D005959:Glucosidases; D013394:Sucrase-Isomaltase Complex; D001616:beta-Galactosidase; D010694:Lactase-Phlorizin Hydrolase; D000626:Aminopeptidases; D018826:CD13 Antigens