alpha-Glucan synthesis on a protein primer, uridine diphosphoglucose: protein transglucosylase I. Separation from starch synthetase and phosphorylase and a study of its properties.
It was found that the DEAE-cellulose-treated UDP-Glc:protein transglucosylase I catalyzing the first step (reaction 1) in the formation of alpha-glucan bound to protein in potato tuber is not only specific for the glucosyl donor but also for the endogenous acceptor. A single radioactive 38-kDa macromolecular component appeared during denaturing polyacrylamide gel electrophoresis of reaction 1 product. The labeled component is probably the polypeptide subunit of the endogenous acceptor which is being glucosylated. The radioactivity incorporated in reaction 1 product was isolated from a protease digest as a low-molecular-mass glucopeptide fraction. A beta-elimination reaction carried out in the presence of a reducing agent demonstrated that only one glucosyl moiety is transferred from UDP-Glc to the aminoacyl residue, thus forming an O-glucosidic linkage. 3H-labeled sodium borohydride showed that serine and threonine are involved in the peptide bond to glucose. Ion-exchange chromatography on DEAE-cellulose, affinity chromatography on concanavalin-A--Sepharose, gel filtration on Sephacryl S-300 and sucrose density gradient centrifugation failed to separate the enzyme catalyzing reaction 1 from the endogenous acceptor.
D000596:Amino Acids / Q000378:metabolism; D002845:Chromatography; D004591:Electrophoresis, Polyacrylamide Gel; D005936:Glucans / Q000096:biosynthesis*; D005964:Glucosyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D012694:Serine / Q000378:metabolism; D011198:Solanum tuberosum; D013379:Substrate Specificity; D013912:Threonine / Q000378:metabolism
D000596:Amino Acids; D005936:Glucans; D010940:Plant Proteins; D013912:Threonine; D012694:Serine; C040088:1,4-glucan; D005964:Glucosyltransferases; C049577:alpha-1,4-glucan-protein synthase (UDP-forming)