N‐terminal sequences of pig intestinal sucrase—isomaltase and pro‐sucrase—isomaltase

Publisher Website
Google Scholar
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 M r 260 000–265 000. 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 in 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.