The Intramolecular Turnover Heterogeneity, a New Property of Plasma Membrane Glycoproteins. Dipeptidylaminopeptidase IV as a Model

摘要: The glyoproteins of the hepatocyte plasma membrane are involved in a variety functions, such as enzymatic activity, antigenicity, receptor and transport function, cellular communication (Hughes 1976). Their actual concentration is regulated by de novo synthesis, insertion into removal from membrane, including an eventual recycling, degradation (for reviews on glycoprotein turnover see Doyle et al. 1982; Hubbard 1978;Blobel 1980; Struck Lennarz 1980). different steps this schematically depicted Fig. 1 (taken Kreisel 1983). Most glycoproteins synthesized membrane-bound polysomes inserted endoplasmatic reticulum membrane. Via dolichol phosphate preliminary carbohydrate chain added, which further processed. finally glycosylated Golgi complex. vesicles transported fuse with (pathway 1). removed mainly internalization units. These may contain random distribution all 2, 3,4); some special molecules, namely receptors, concentrated coated pits Open image new window Fig. 1 Fig. 1. Pathways turn-over details text). SER, smooth reticulum; RER, rough reticulum vesicles