Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The highese disaccharidase activity for sucrose maltose and maltitol was found in the jejunum, followed by the ileum and duodenum. However, the disaccharidase activity for maltitol was extremely low compared with that for sucrose and maltose. 2. For maltitol, the Km value was very large and the Vmax value was very low compared compared with the values for sucrose and maltose. 3. The initial velocity (v) in the presence of the sucrose and maltitol, was equal to the sum of the rates for individual substrates sucrose ann maltitol (v1, v2) respectively (v=v1+v2). Thus, no competition between these substrates was observed. In the case of maltose and maltitol, the initial velocity (v) in the presence of both substrates was less than the sum of the individual rates for maltose and maltitol (v1, v2) in the absence of the other substrate (v is less than v1 + v2). This finding demonstrates that there is competition between these two substrates for the same enzyme. Furthermore, the apparent Michaelis constant (Km) and the apparent maximal velocity (Vmax) for pure and mixed substrates, i.e., maltose and maltitol, at various mole fractions of maltose showed dependence on the mole fraction of maltose. The obtained kinetic data provide strong evidence that both maltose and maltitol react at the single active center of maltase.
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PMID:The effects of maltitol on rat intestinal disaccharidases. 115 99

Crystalline, alpha-glucosidase-free sweet potato beta-amylase was found to catalyze hydration of the enolic bond of maltal (alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-glucal) to form 2-deoxymaltose (alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-glucose). The reaction at pH 5.0 showed Vmax 0.082 mumol/min/mg and km 94.5 mM. An exceptionally large solvent deuterium isotope effect, VH/VD = 8, was observed from pH(pD) 4.2 to 5.4; and at pH(pD) 5.0 the effect was found to be directly related to the mole fraction of 2H. The hydration product, isolated from a beta-amylase/maltal digest in acetate-d4/D2O buffer (pD 5.4) was identified through its 1H NMR spectrum as alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-[2(a)-2H]glucose. beta-Amylase in 2H2O thus catalyzes deuteration of the double bond of maltal from a direction opposite that assumed for protonation of the glycosidic oxygen atoms of starch chains and maltosaccharides. This finding confirms the functional flexibility of the enzyme's catalytic groups first demonstrated in studies of the reactions catalyzed with alpha- and beta-maltosyl fluoride (Hehre, E. J., Brewer, C. F., and Genghof, D. S. (1979) J. Biol. Chem. 254, 5942-5950). A possible mechanism of the maltal hydration by beta-amylase involves protonation of substrate from above as the first and rate-limiting step, followed by formation of a transient carbonium ion-enzyme intermediate. Although other possible mechanisms cannot be ruled out, it is clear that this hydration reaction differs from reactions catalyzed with amylaceous substrates and with alpha- and beta-maltosyl fluoride. The ability of beta-amylase to catalyze different types of reactions with different substrates is discussed with respect to observations with other enzymes that, likewise, strongly support the view (Hehre et al.) that the catalytic groups of glycosylases in general may be functionally flexible beyond requirements of the principle of microscopic reversibility.
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PMID:Catalytic flexibility of glycosylases. The hydration of maltal by beta-amylase to form 2-deoxymaltose. 241 22

Premature infants are susceptible to intestinal ischemia during the newborn period when their intestinal tracts are functionally and structurally immature. Studies have shown that exogenous glucocorticoids hasten intestinal maturation. We investigated the effects of hydrocortisone on platelet activating factor (PAF)-induced intestinal ischemia in the neonatal rat. On Postnatal Days 7-11, Sprague-Dawley rats were given intraperitoneal (ip) injections of either saline (SAL) or hydrocortisone (HC; 50 mg/kg total). On Day 12, rats were injected with either PAF (2 micrograms/kg) or an equal volume of saline. After 2 hr the rats were sacrificed and sections were taken for histology. The remaining intestine was analyzed for maltase, lactase, myeloperoxidase (MPO), and xanthine oxidase (XO). Experimental groups were as follows: SAL (N = 8), received saline only; SAL+PAF (N = 8), received saline plus PAF; HC (N = 3), received hydrocortisone+saline; and HC+PAF (N = 5), received hydrocortisone plus PAF. XO was significantly decreased (P < 0.001) in the hydrocortisone-treated groups (HC + SAL = 16.36 +/- 18.42 units/g protein, HC + PAF = 17.33 +/- 9.06 units/g protein) vs the controls (SAL only = 108.90 +/- 20.24 units g/protein, SAL + PAF = 145.77 21.28 units/g protein). MPO was not significantly elevated in SAL + PAF (4.60 +/- 0.95 units/g protein) vs HC + PAF (2.18 +/- 0.80 units/g protein) in this study. Maltase was significantly elevated (P < 0.001) in the HC + PAF (241.46 +/- 40.6 mole/min/g protein) and HC + SAL (152.78 +/- 16.35 mole/min/g protein) vs saline only (28.35 +/- 5.77 mole/min/g protein and SAL + PAF (37.29 +/- 8.70 mole/min/g protein. Animals (7/8) in the SAL + PAF group developed ischemia by inspection and histologic exam.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Intestinal ischemia in the newborn: the role of intestinal maturation. 824 92

The catalytic amino acid residue of Aspergillus niger alpha-glucosidase (ANGase) was identified by modification with conduritol B epoxide (CBE), a mechanism-based irreversible inactivator. The inactivation by CBE followed pseudo-first order kinetics. The interaction of CBE and ANGase conformed to a model with a reversible enzyme-inhibitor complex formed before covalent inactivation. A competitive inhibitor, Tris, decreased the inactivation rate. The incorporation of one mole of CBE per mole of ANGase was completely abolished the enzyme activity. A dissociated carboxyl group (-COO-) in the active site was suggested to attack the C-1 of CBE. ANGase was composed of two subunits (P1 and P2), of which P2 was modified by CBE. The labelled residue was included in a peptide (LY3) that was obtained from Lys-C protease digestion of CBE-bound P2. The sequence analysis of CBE-labelled LY3 showed that an Asp was the modified residue, that is, one of the catalytic amino acid residues of ANGase. The primary structure of LY3 was determined by analyzing the sequence of peptide fragments prepared by several proteases.
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PMID:A catalytic amino acid and primary structure of active site in Aspergillus niger alpha-glucosidase. 925 70