title: N-Terminal sequences of pig intestinal sucrase-isomaltase and pro-sucrase--isomaltase. Implications for the biosynthesis and membrane insertion of pro-sucrase--isomaltase.
abstract: The hog sucrase-isomaltase complex is anchored to the small-intestinal brush border membrane, as in the rabbit, via a hydrophobic segment located in the N-terminal region of the isomaltase subunit. The immediate precursor of the 'final' sucrase-isomaltase (i.e., pro-sucrase-isomaltase as prepared from adult hogs whose pancreas had been disconnected from the duodenum) is an amphiphilic single polypeptide chain of Mr 260000-265000. Its N-terminal sequence is virtually identical with (not merely homologous to) the corresponding region of the isomaltase subunit of 'final' sucrase-isomaltase. This shows that the isomaltase portion of pro-sucrase-isomaltase is the N-terminal 'half' of the precursor polypeptide chain. Thus the succession of domains in pro-sucrase-isomaltase and its mode of anchoring in the membrane could be deduced. On this basis a likely mechanism of biosynthesis and insertion is proposed.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology*; D004792:Enzyme Precursors / Q000096:biosynthesis*; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology*; D008871:Microvilli / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000096:biosynthesis*; D011817:Rabbits; D051381:Rats; D013045:Species Specificity; D013394:Sucrase-Isomaltase Complex / Q000096:biosynthesis*; D013552:Swine
chemical_list: D004792:Enzyme Precursors; D009097:Multienzyme Complexes; D013394:Sucrase-Isomaltase Complex