Small Intestinal mRNA Research Articles

Biosynthesis of intestinal microvillar proteins Effect of castanospermine on cell-free synthesis of aminopeptidase N

Pig small intestinal mRNA was translated in a rabbit reticulocyte lysate system supplemented with microsomal membranes. Castanospermine, an inhibitor of glucosidase I, induced a high mannose-glycosylated form of microvillar aminopeptidase N(EC 3.4.11.2) of increased molecular mass, indicating the blocked removal of glucose residues. In contrast to its reduced expression in a mucosal explant system [(1986) Biochem. J. 240, 777–782], this molecular form of aminopeptidase N was at least as abundant in cell-free translation as its normal high mannose-glycosylated counterpart, ruling out degradation taking place in the rough endoplasmic reticulum. Degradation of newly produced malprocessed enzyme must therefore occur at a later stage during intracellular transport, presumably in the sarcoplasmic reticulum or in transitional elements between this organelle the Golgi complex.

Expression of transporters in Xenopus oocytes.

Xenopus oocytes were injected with exogenous mRNA prepared from rat small intestine and kidney and their electrical responses to glucose and amino acids were measured electrophysiologically. Na+/glucose, amino acid cotransporters were expressed in the oocytes by injection of small intestine mRNA, while facilitated diffusion carrier protein(s) (uniporter) were mainly expressed by injection of kindney mRNA.