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Gene Review

SI  -  sucrase-isomaltase (alpha-glucosidase)

Homo sapiens

Synonyms: Sucrase-isomaltase, intestinal
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Disease relevance of SI


High impact information on SI

  • Unlike its counterpart in normal controls, pro-SI in this phenotype is intracellularly cleaved [2].
  • By contrast to normal controls, however, pro-SI does not undergo terminal glycosylation in the Golgi apparatus [2].
  • Subcellular localization of pro-SI by immunoelectron microscopy revealed unusual labeling of the molecule in the basolateral membrane and no labeling in the brush border membrane thus indicating that pro-SI is missorted to the basolateral membrane [2].
  • SI gene cassettes with an identifiable activity encode proteins related to simple adaptive functions, including resistance, virulence, and metabolic activities, and their recruitment was interpreted as providing the host with an adaptive advantage [3].
  • 0-kilobase (kb) sucrase-isomaltase (SI, EC cDNA from suncus intestinal cDNA library [4].

Biological context of SI

  • While the cells transfected with the plasmids expressing SI in the KAT line showed both sucrase and isomaltase activity, the plasmids expressing MI line cDNA showed only isomaltase activity [4].
  • The deduced amino-acid sequence of rat SI predicts a 230-residue protein (26737 Da) with 87% and 80% amino-acid identity to mouse and human counterparts [1].
  • The rat SI gene was mapped to chromosome 12q1.2 using fluorescence in situ hybridization (FISH) [1].
  • Using hierarchical regression analysis, the mean motor unit action potential (MUAP) size index (SI) and the amount of PSA were accurate predictors of T1-weighted signal intensity in MRI, an expression of fatty degeneration [5].
  • RESULTS: The linear combination of size and irregularity measures, i.e. size index (SI) and irregularity coefficient (IR) obtained using Principal Component Analysis (PCA) did not increase the discriminating ability in comparison to SI [6].

Anatomical context of SI

  • The FISH studies revealed ubiquitous expression of SI mRNA in rat hepatocytes [1].

Associations of SI with chemical compounds

  • The second phenotype revealed two variants of pro-SI precursors that differ in their content of mannose-rich oligosaccharides [2].
  • The in vivo experiments also indicate that both mRNA expression and enzymic activity of SI in liver were induced approx. 3-fold in rats fed 5% (w/w) cholestyramine plus 0.1% (w/w) lovastatin in normal chow for 2 weeks [1].
  • The in vitro studies showed that the SI mRNA was highly suppressed by 25-hydroxycholesterol in H4IIE cells [1].
  • It showed a characteristic pattern of inhibition on exposure to trans-2-[4-(1,2-diphenylbuten-1-yl)phenoxy]-N,N-dimethylethylamine (tamoxifen; IC(50)=11.2 microM) and 3beta-[2-(diethylamino)ethoxy]androst-5-en-17-one (U18666A; IC(50)=4.2 microM), two well known potent inhibitors of SI [1].
  • To investigate the in vitro and in vivo modes of molecular regulation of SI and its role in cholesterol biosynthesis in mammals, we isolated a full-length cDNA encoding rat SI [1].

Analytical, diagnostic and therapeutic context of SI


  1. Cholesterol biosynthesis from lanosterol: molecular cloning, chromosomal localization, functional expression and liver-specific gene regulation of rat sterol delta8-isomerase, a cholesterogenic enzyme with multiple functions. Bae, S., Seong, J., Paik, Y. Biochem. J. (2001) [Pubmed]
  2. Naturally occurring mutations in intestinal sucrase-isomaltase provide evidence for the existence of an intracellular sorting signal in the isomaltase subunit. Fransen, J.A., Hauri, H.P., Ginsel, L.A., Naim, H.Y. J. Cell Biol. (1991) [Pubmed]
  3. Comparative analysis of superintegrons: engineering extensive genetic diversity in the Vibrionaceae. Rowe-Magnus, D.A., Guerout, A.M., Biskri, L., Bouige, P., Mazel, D. Genome Res. (2003) [Pubmed]
  4. Molecular cloning of sucrase-isomaltase cDNA in the house musk shrew Suncus murinus and identification of a mutation responsible for isolated sucrase deficiency. Ito, T., Hayashi, Y., Ohmori, S., Oda, S., Seo, H. J. Biol. Chem. (1998) [Pubmed]
  5. Correlation between quantitative EMG and muscle MRI in patients with axonal neuropathy. Jonas, D., Conrad, B., Von Einsiedel, H.G., Bischoff, C. Muscle Nerve (2000) [Pubmed]
  6. The SIIR index--a non-linear combination of waveform size and irregularity parameters for classification of motor unit potentials. Zalewska, E., Hausmanowa-Petrusewicz, I. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. (2005) [Pubmed]
  7. Motor unit action potential (MUAP) parameters affected by editing duration cursors. Takehara, I., Chu, J., Schwartz, I., Aye, H.H. Electromyography and clinical neurophysiology. (2004) [Pubmed]
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