Disease relevance of Si

• The enterocyte markers, sucrase-isomaltase, sodium-glucose co-transporter 1, glucose transporters 2 and 5, and intestinal and liver fatty acid binding protein, were down-regulated after MTX in NP epithelium but not in PP epithelium [1].
• An abnormally high level of the sucrase-isomaltase (SI) complex in the small intestine of rats with streptozotocin-induced insulin-dependent diabetes mellitus (IDDM) was normalized in 11 h by the administration of insulin, in addition to normalization of the blood glucose level [2].
• Rat small intestinal epithelial cells and human colon adenocarcinoma cells cultured on Matrigel expressed the differentiation specific enzyme, sucrase-isomaltase, as determined by indirect immunofluorescence [3].
• Disordered expression of the sucrase-isomaltase complex in the small intestine in Otsuka Long-Evans tokushima fatty rats, a model of non-insulin-dependent diabetes mellitus with insulin resistance [4].

Psychiatry related information on Si

• Sucrase expression was further increased by prolonged food deprivation, whereas enzyme activity as well as the amount of SI mRNA dropped to reach the low level found in control sucklings when 48 h-starved pups were refed by returning them to their dams [5].

High impact information on Si

• The intestinal brush border membrane in diabetes. Studies of sucrase-isomaltase metabolism in rats with streptozotocin diabetes [6].
• METHODS: Enzyme activity, Northern analysis, and electrophoretic mobility shift assays were used to study the relationship of these nuclear proteins to sucrase-isomaltase and lactase-phlorizin hydrolase gene expression in rats during development [7].
• In contrast, sucrase-isomaltase was first detected at 16 days, with patchy expression along the total small intestine; at 21 days it was abundant [8].
• METHODS: The topographical regulation of lactase was studied in conjunction with sucrase-isomaltase in proximal, middle, and distal segments of 0-, 7-, 14-, 16-, 18-, 21-, and 28-day-old and adult rats using in sity hybridization, immunohistochemistry, and ribonuclease protection assays [8].
• The intestinal sucrase-isomaltase precursor is cleaved at the brush border membrane by luminal proteases [9].

Biological context of Si

• Biosynthesis of sucrase-isomaltase. Purification and NH2-terminal amino acid sequence of the rat sucrase-isomaltase precursor (pro-sucrase-isomaltase) from fetal intestinal transplants [10].
• At the active sites of both S and I, the rat nt sequence encodes stretches of 14 and 16 aa, respectively, which show 100% identity to rabbit and human SI [11].
• We isolated a 6.1-kb SI cDNA clone (GC1.4) from a size-fractionated cDNA library from rat intestine [11].
• Regulation of sucrase-isomaltase gene expression along the crypt-villus axis of rat small intestine [12].
• Biogenesis of intestinal plasma membrane: posttranslational route and cleavage of sucrase-isomaltase [13].

Anatomical context of Si

• The dimeric enzyme sucrase-isomaltase (a complex of sucrose alpha-glucohydrolase, EC 3.2.1.48 and oligo-1,6-glucosidase (dextrin 6 alpha-D-glucanohydrolase), EC 3.2.1.10) of the rat small intestinal microvillus membrane is synthesized as a single chain enzymatically active precursor protein [10].
• Sucrase-isomaltase (SI) has been widely used as a marker enzyme to study cellular differentiation in the small intestine [11].
• We conclude that expression of sucrase-isomaltase as enterocytes emerge from intestinal crypts is regulated primarily at the level of mRNA accumulation which, most likely, is a result of activation of sucrase-isomaltase gene transcription [12].
• To investigate the regulation of expression of intestinal sucrase-isomaltase (SI) complex in response to sucrose feeding, we isolated a cDNA (RPSI1) encoding partially the pro-SI of rat intestinal mucosa [14].
• Synthesis and intracellular processing of sucrase-isomaltase in rat jejunum [15].

Associations of Si with chemical compounds

• The apical sorting of the small intestinal membrane glycoprotein sucrase-isomaltase (SI) depends on the presence of O-linked glycans and the transmembrane domain [16].
• The NH2-terminal sequence of purified pro-sucrase-isomaltase was identical with that of the isolated isomaltase subunit which possesses the membrane anchor for the mature enzyme complex but differed from the NH2-terminal sequence of the sucrase subunit [10].
• We conclude that the O-glycans in the stalk region of SI act as an apical sorting signal within a sorting machinery that comprises at least a carbohydrate-binding protein and fulfills specific spatial requirements provided, for example by a polyglycine spacer in the context of rGH or the P-domain within the SI enzyme complex [16].
• Recently, we cloned a cDNA (NaSi-1) localized to rat renal proximal tubules and encoding the brush-border membrane (BBM) Na gradient-dependent inorganic sulfate (Si) transport protein (Na-Si cotransporter) [17].
• Lactase synthesis and processing was studied in 0- and 15-day-old rats after IP administration of [35S]methionine, and changes in precociously cortisone-induced sucrase-isomaltase were used as an internal control [9].

Physical interactions of Si

• This applies particularly to the sucrase-isomaltase complex and the lactase-beta-glucosidase complex [18].

Regulatory relationships of Si

• An increase in alkaline phosphatase and lactase activity was observed after 3-4 days in these colonies which could be enhanced to yield 90%-100% positive cells by the addition of dexamethasone to the medium while no sucrase-isomaltase activity was elicited [19].

Other interactions of Si

• Addition of trypsin or elastase into the lumen of flushed segments resulted in partial cleavage of lactase precursor but not of sucrase-isomaltase precursor [9].
• The 142- and 130-kDa adducts of diclofenac were identified as aminopeptidase N (CD13) and sucrase-isomaltase, respectively, by amino acid sequence analyses and by their reactions with protein-specific antibodies [20].
• Glucagon-like peptide-2 increases sucrase-isomaltase but not caudal-related homeobox protein-2 gene expression [21].
• We previously demonstrated that the levels of mRNAs of both sucrase-isomaltase (SI) and sodium/D-glucose transporter (SGLT1) are modulated by dietary sucrose in the rat jejunum [22].
• ClC-5 partially colocalized with the transcytosed polymeric immunoglobulin receptor but was not detectable together with the brush-border-anchored sucrase isomaltase [23].

Analytical, diagnostic and therapeutic context of Si

• In situ hybridization using 35[S]-labeled RNA probes demonstrated that autoradiographic grains were detected over eptithelial cells located on villi with the greatest number of grains located at the crypt-villus junction and in the lower to mid-villus region; from mid-villus to the villus tip there was a decline in sucrase-isomaltase mRNA [12].
• Northern blot analysis revealed that the mRNA levels of SI increased rapidly after sucrose force feeding, while those of rats fed a carbohydrate-free diet did not [14].
• Molecular cloning and characterization of a rat intestinal sucrase-isomaltase cDNA. Regulation of sucrase-isomaltase gene expression by sucrose feeding [14].
• We used immune electron microscopy to study the intracellular localization of sucrase-isomaltase, an intrinsic glycoprotein of the brush border membrane, to provide insight regarding the sites of its synthesis and intracellular processing and the mechanisms of its transfer to the brush border membrane [24].
• Mucosal lactase and sucrase-isomaltase were separately immunoprecipitated and analyzed by autoradiography after electrophoresis [9].

References