Topic 8.11

Glossary of Carbohydrate Biochemistry

ADPG pyrophosphorylase [EC 2.7.7.27] catalyzes ATP + α-D-glucose 1-phosphate → pyrophosphate + ADP-glucose.

aldose: a sugar with a terminal aldehyde.

α-amylase [EC 3.2.1.1] catalyzes the endohydrolysis of α-D-1,4 glucosidic linkages in polysaccharides containing three or more 1,4-α-linked D-glucose units. The term ′α′ indicates the initial anomeric configuration of the free sugar group released and not the configuration of the linkage hydrolysed.

β-amylase [EC 3.2.1.2] catalyzes the hydrolysis of β-D-1,4 glucosidic linkages in polysaccharides so as to remove successive maltose units from the nonreducing ends of the chains. The term ′β′ denotes the initial anomeric configuration of the free sugar group released and not the configuration of the linkage hydrolysed.

β-amylolysis: the stepwise hydrolysis of alternate glucosidic bonds in starch-type polysaccharides with the liberation of maltose.

amylopectin: the constituent of starch having a polymeric, branched structure in which an α-D-1,6 bond occurs every 20–30 glucose units linked via α-D-1,4 bonds.

amylose: The constituent of starch in which α-D-1,4 glucosidic bonds form linear chains of 200–2000 glucose units.

anomer: epimers that differ only in the configuration at the carbonyl carbon -(C=O)- of aldoses or ketoses.

dextranase [EC 3.2.1.11] catalyzes the endohydrolysis of α-D-1,6 glucosidic linkages in dextran.

disproportionating enzyme [EC 2.4.1.25, D-enzyme] catalyzes the transfer of a segment of an α-D-1,4 glucan to a new position in an acceptor, which may be glucose or a 1,4-linked α-D-glucan.

epimers: a pair of isomers that differ from each other only in their configuration at a single asymetric center.

α-(1,4)-glucan branching enzyme [EC 2.4.1.18, branching enzyme; Q-enzyme] catalyzes the transfer of a segment of an α-D-1,4-linked glucan chain to a primary hydroxyl group in a similar glucan chain.

α-glucosidase [EC 3.2.1.20, maltase] catalyzes the hydrolysis of terminal, nonreducing 1,4-linked α-D-glucose residues with the release of α-D-glucose.

glycosidic bond: a bond between the C-1 of glucose and the oxygen atom of another hexose moeity sugars can be linked to each other by O-glycosidic bonds to form oligo- and polysaccharides.

isoamylase [EC 3.2.1.68, debranching enzyme] catalyzes the hydrolysis of α-D-1,6 glucosidic branch linkages in glycogen, amylopectin, and their β-limit dextrins.

ketose: sugar with a terminal ketone group.

limit dextrinase [EC 3.2.1.142, R-enzyme] catalyzes the hydrolysis of α-D-1,6 glucosidic linkages in α- and β-limit dextrins of amylopectin and glycogen, and in amylopectin and pullulan.

malto-oligosaccharides (maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose): the series of linear oligosaccharides composed of two, three, four, five and six, respectively, units of glucose all linked via an α-D-1,4 bond.

maltose phosphorylase [EC 2.4.1.8] catalyzes the phosphorolysis of maltose yielding D-glucose and β-D-glucose 1-phosphate.

nonreducing end: the extreme of the polysaccharide chain that holds the aldol C-1 of the hexose moeity (oxidized with alkaline copper).

phosphorolysis: the cleavage of a glycosidic linkage by the addition of a phosphoryl group to one of the products.

phytoglycogen: a minor constituent of starch having a branched structure in which an α-D-1,6 bond occurs every 10–15 glucose units linked via α-D-1,4 bonds.

14-3-3 proteins: phosphoserine-binding proteins that regulate the activities of a wide array of targets via direct protein–protein interactions. The 14-3-3 proteins were first identified as abundant brain proteins and named after their elution position on ion exchange chromatography and mobility in starch gel electrophoresis.

pullulanase [EC 3.2.1.41, debranching enzyme] catalyzes the hydrolysis of α-D-1,6 glucosidic linkages in pullulan [a linear polymer of α-1,6-linked maltotriose units] and in amylopectin and glycogen, and the α- and β-limit dextrins of amylopectin and glycogen.

SnRK1: The plant protein SnRK1 is homologous to the product of the SNF1 (sucrose non-fermenting-1) gene that was identified genetically in screenings of budding yeast mutants. These variants fail to express the invertase gene, SUC2, in response to glucose deprivation. SnRK1 phosphorylates and, in so doing, inactivates in vitro sucrose 6^F-phosphate phosphatase, 3-hydroxy-3-methylglutaryl-Coenzyme A reductase (linked to sterol/isoprenoid synthesis), and nitratereductase (associated to nitrogen assimilation).

starch phosphorylase [EC 2.4.1.1] catalyzes the phosphorolysis of (α-D-1,4 glucosyl)_n yielding (α-D-1,4 glucosyl)_n–1 and α-D-glucose 1-phosphate.

starch synthase [EC 2.4.1.21] catalyzes the reaction: ADP-glucose + (α-D-1,4 glucosyl)_n → ADP + (α-D-1,4 glucosyl)_n+₁.