Glucomannan synthesis in pea epicotyls: the mannose and glucose transferases.
Membrane fractions and digitonin-solubilized enzymes prepared from stem segments isolated from the third internode of etiolated pea seedlings (Pisum sativum L. cv. Alaska) catalyzed the synthesis of a beta-1,4-[14C]mannan from GDP-D-[U-14C]-mannose, a mixed beta-1,3- and beta-1,4-[14C]glucan from GDP-D-[U-14C]-glucose and a beta-1,4-[14C]-glucomannan from both GDP-D-[U-14C]mannose and GDP-D-[U-14C]glucose. The kinetics of the membrane-bound and soluble mannan and glucan synthases were determined. The effects of ions, chelators, inhibitors of lipid-linked saccharides, polyamines, polyols, nucleotides, nucleoside-diphosphate sugars, acetyl-CoA, group-specific chemical probes, phospholipases and detergents on the membrane-bound mannan and glucan synthases were investigated. The beta-glucan synthase had different properties from other preparations which bring about the synthesis of beta-1,3-glucans (callose) and mixed beta-1,3- and beta-1,4- glucans and which use UDP-D-glucose as substrate. It also differed from xyloglucan synthase because in the presence of several concentrations of UDP-D-xylose in addition to GDP-D-glucose no xyloglucan was formed. Using either the membrane-bound or the soluble mannan synthase, GDP-D-glucose acted competitively in the presence of GDP-D-mannose to inhibit the incorporation of mannose into the polymer. This was not due to an inhibition of the transferase activity but was a result of the incorporation of glucose residues from GDP-D-glucose into a glucomannan. The kinetics and the composition of the synthesized glucomannan depended on the ratio of the concentrations of GDP-D-glucose and GDP-D-mannose that were available. Our data indicated that a single enzyme has an active centre that can use both GDP-D-mannose and GDP-D-glucose to bring about the synthesis of the heteropolysaccharide.
Piro
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Dipartimento di Biologia, Università di Lecce, Italy.
Zuppa
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A
Dalessandro
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Northcote
D H
DH
D000105:Acetyl Coenzyme A / Q000494:pharmacology; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism; D004072:Digitonin; D007887:Fabaceae / Q000201:enzymology / Q000378:metabolism*; D005936:Glucans / Q000096:biosynthesis; D005964:Glucosyltransferases / Q000378:metabolism*; D006155:Guanosine Diphosphate Mannose / Q000378:metabolism; D006156:Guanosine Diphosphate Sugars / Q000378:metabolism; D007700:Kinetics; D008351:Mannans / Q000096:biosynthesis*; D008364:Mannosyltransferases / Q000378:metabolism*; D008566:Membranes / Q000201:enzymology; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000494:pharmacology; D010946:Plants, Medicinal; D013096:Spermine / Q000494:pharmacology; D014532:Uridine Diphosphate Glucose / Q000494:pharmacology; D014540:Uridine Diphosphate Xylose / Q000494:pharmacology
D002241:Carbohydrates; D002413:Cations, Divalent; D005936:Glucans; D006156:Guanosine Diphosphate Sugars; D008351:Mannans; D009711:Nucleotides; C081692:beta-1,4-mannan; D013096:Spermine; D006155:Guanosine Diphosphate Mannose; D014540:Uridine Diphosphate Xylose; C100085:guanosine diphosphate glucose; D000105:Acetyl Coenzyme A; D005964:Glucosyltransferases; D008364:Mannosyltransferases; C021542:mannan synthetase; D004072:Digitonin; D014532:Uridine Diphosphate Glucose