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At least 1,171 records · Page 65Linked to original sources
PubMed1998

Intestinal Na+/glucose cotransporter-mediated transport of glucose conjugate formed from disaccharide conjugate.

Intestinal absorption of beta-disaccharide (cellobiose, maltose and lactose) conjugates of p-nitrophenol (p-nitrophenyl beta-disaccharide) were examined in terms of the hydrolysis of disaccharide conjugate to monosaccharide conjugate and the transport of monosaccharide conjugate by Na+/glucose transport carrier (SGLT1). beta-Cellobioside, beta-maltoside and beta-lactoside of p-nitrophenol (p-NP) were hydrolyzed to p-nitrophenyl beta-glucoside (p-NPbeta glc) on the mucosal side, and p-NPbeta glc appeared on the serosal side. Although p-NP beta-disaccharide, p-NP and p-NP glucuronide also appeared on the serosal side, their amounts were much lower than that of p-NPbeta glc. The amount of p-NPbeta glc transported to the serosal side was decreased in the presence of phloridzin (transport inhibitor of SGLT1) and in the absence of Na+ (a cosubstrate of SGLT1), indicating that p-NPbeta glc was formed from p-NP beta-disaccharide on the mucosal side and transported to the serosal side by SGLT1. Furthermore, the absorption clearance of p-NPbeta glc, which was formed from p-NP beta-cellobioside and p-NP beta-lactoside by lactase-phloridzin hydrolase (LPH), was much higher than that of p-NPbeta glc itself, although the absorption clearance of p-NPbeta glc, which was formed from p-NP beta-maltoside by maltase was similar to that of p-NPbeta glc itself. These results indicated that p-NPbeta glc was transported by the vectorial cooperation of SGLT1 with LPH from mucosal p-NP beta-cellobioside or p-NP beta-lactoside.

Animals↗
PubMed2000

Identification of Asp-130 as the catalytic nucleophile in the main alpha-galactosidase from Phanerochaete chrysosporium, a family 27 glycosyl hydrolase.

Characterization of the complete gene sequence encoding the alpha-galactosidase from Phanerochaete chrysosporium confirms that this enzyme is a member of glycosyl hydrolase family 27 [Henrissat, B., and Bairoch, A. (1996) Biochem. J. 316, 695-696]. This family, together with the family 36 alpha-galactosidases, forms glycosyl hydrolase clan GH-D, a superfamily of alpha-galactosidases, alpha-N-acetylgalactosaminidases, and isomaltodextranases which are likely to share a common catalytic mechanism and structural topology. Identification of the active site catalytic nucleophile was achieved by labeling with the mechanism-based inactivator 2',4', 6'-trinitrophenyl 2-deoxy-2,2-difluoro-alpha-D-lyxo-hexopyranoside; this inactivator was synthesized by anomeric deprotection of the known 1,3,4,6-tetra-O-acetyl-2-deoxy-2, 2-difluoro-D-lyxo-hexopyranoside [McCarter, J. D., Adam, M. J., Braun, C., Namchuk, M., Tull, D., and Withers, S. G. (1993) Carbohydr. Res. 249, 77-90], picrylation with picryl fluoride and 2, 6-di-tert-butylpyridine, and O-deacetylation with methanolic HCl. Enzyme inactivation is a result of the formation of a stable 2-deoxy-2,2-difluoro-beta-D-lyxo-hexopyranosyl-enzyme intermediate. Following peptic digestion, comparative liquid chromatographic/mass spectrometric analysis of inactivated and control enzyme samples served to identify the covalently modified peptide. After purification of the labeled peptide, benzylamine was shown to successfully replace the 2-deoxy-2,2-difluoro-D-lyxo-hexopyranosyl peptidyl ester by aminolysis. The labeled amino acid was identified as Asp-130 of the mature protein by further tandem mass spectrometric analysis of the native and derivatized peptides in combination with Edman degradation analysis. Asp-130 is found within the sequence YLKYDNC, which is highly conserved in all known family 27 glycosyl hydrolases.

Amino Acid Sequence↗
PubMed1965

HYDROLYSIS OF FIBROUS COTTON AND REPRECIPITATED CELLULOSE BY CELLULOLYTIC ENZYMES FROM SOIL MICRO-ORGANISMS.

1. The action of cell-free filtrates from Trichoderma koningii was examined on undegraded cellulose in the form of cotton fibres, on degraded cellulose in the form of cellulose powder reprecipitated from phosphoric acid and on the soluble cellulose derivative CM-cellulose. 2. The cell-free filtrates compare favourably with intact cellulolytic micro-organisms in producing complete solubilization of undegraded as well as of degraded types of cellulose. Enzymic solubilization of cotton fibres gives quantitative conversion into glucose. Cellobiase is present. 3. The early enzymic breakdown of cotton fibres is characterized by the formation of very short fibres that increase to a maximum and disappear gradually by conversion into glucose. Disintegration of cotton fibres to short fibres is assisted by shaking, and within 20hr. the enzyme converts a minor fraction (up to 16%) of substrate into soluble products and a major portion (80%) into insoluble short fibres. 4. Maximum enzymic activity on cotton fibres occurs at about pH5.0, measured by the formation of short fibres, and at about pH3.8 on reprecipitated cellulose, measured by solubilization of the substrate. 5. Gluconolactone, glucose and cellobiose fail to produce marked inhibition of the enzymic hydrolysis of cotton fibres to short fibres or of the solubilization of reprecipitated cellulose unless present in amounts comparable with or greater than the initial weight of these two forms of cellulose. 6. The heavy-metal ions Cu(2+), Hg(2+) and Fe(3+) at 2mm concentration give 80-100% decrease in the enzymic breakdown of cotton fibres, measured by the formation of short fibres. At the same concentration Hg(2+) and Fe(3+) but not Cu(2+) also produce 70-100% inhibition of the solubilization of reprecipitated cellulose. 7. The ability to hydrolyse cotton fibres to short fibres and CM-cellulose to sugars is completely lost after heating enzyme preparations for 10min. at 71 degrees .

Cellulose↗