Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.52 (PNGase F)
 1,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The biosynthesis and maturation of human sucrase-isomaltase (SI, EC 3.2.1.48-10), was studied in cultured small intestinal biopsy specimens and mucosa explants. Pulse-chase experiments with [35S]methionine revealed one high mannose intermediate of Mr = 210,000 (pro-SIh) which was processed at a slow rate to an endo H-resistant, mature form of Mr = 245,000 (pro-SIc). The fully core-glycosylated form (Mr = 212,000) was detected only when 1-deoxynojirimycin was added to the culture medium, thus indicating that the core sugars undergo rapid processing by rough endoplasmic reticulum membrane-bound glycosidases. The data presented showed that trypsin specifically and instantaneously (within 1 min) cleaves pro-SIc to two subunits Ic (Mr = 145,000) and Sc (Mr = 130,000). Elastase and chymotrypsin are not effective. Enzymic and chemical deglycosylations of SI with endo-beta-N-acetylglucosaminidase F/glycopeptidase F and trifluoromethanesulfonic acid (TFMS) as well as probing for the binding capacity of SI to Helix pomatia lectin demonstrated that pro-SIc, Ic, and Sc are N- and O-glycosylated. Furthermore, the results were indicative of a posttranslational O-glycosylation of pro-SI, since (i) the earliest detectable precursor form, pro-SIh, did not bind to H. pomatia lectin and (ii) its deglycosylation products with both endo-beta-N-acetylglucosamidase H and TFMS were identical. Both the Sc and Ic subunits contain eight N-linked glycan units, at least one of which is of the high mannose type and found on Sc. Finally, Sc, but not Ic, was shown to display at least four populations varying in their content of O-linked glycans. The heterogeneous O-glycosylation pattern of Sc could be correlated with the distal position of this subunit (and its O-glycosylation sites) within the pro-SI molecule, thus affecting the extent of O-linked oligosaccharide processing and their subsequent presentation on the mature molecule.
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PMID:Biosynthesis of the human sucrase-isomaltase complex. Differential O-glycosylation of the sucrase subunit correlates with its position within the enzyme complex. 336 77

A 127-kDa protein was identified as a component of the H+/oligopeptide transport system in brush-border membrane vesicles from rabbit small intestine by photoaffinity labeling with [3H]cephalexin and further photoreactive beta-lactam antibiotics and dipeptides. Reconstitution of stereospecific transport activity revealed the involvement of the 127-kDa protein in H+-dependent transport of oligopeptides and orally active alpha-amino-beta-lactam antibiotics (Kramer et al., Eur. J. Biochem. 204 (1992) 923-930). H+-Dependent transport activity was found in all segments of the small intestine concomitantly with the specific labeling of the 127-kDa protein. By enzymatic deglycosylation, fragments of Mr 116 and 95 kDa were obtained from the 127-kDa protein with endoglucosidase F and N-glycanase, whereas with endoglucosidase H, a fragment of Mr 116 kDa was formed. These findings indicate that the photolabeled 127-kDa protein is a microheterogenous glycoprotein. Surprisingly, it was found that the solubilized and purified 127-kDa protein showed enzymatic sucrase and isomaltase activity. Inhibition of the glucosidase activities with the glucosidase inhibitor HOE 120 influenced neither H+/oligopeptide transport nor photoaffinity labeling of the 127-kDa protein. With polyclonal antibodies raised against the purified 127-kDa protein, a coprecipitation of sucrase activity and the photolabeled 127-kDa beta-lactam antibiotic binding protein occurred. Target size analysis revealed a functional molecular mass of 165+/-17 kDa for photoaffinity labeling of the 127-kDa protein, suggesting a homo- or heterodimeric functional structure of the 127-kDa protein in the brush-border membrane. These findings indicate that the H+/oligopeptide binding protein of Mr 127000 is closely associated with the sucrase/isomaltase complex in the enterocyte brush-border membrane.
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PMID:Structural studies of the H+/oligopeptide transport system from rabbit small intestine. 973 62