Cyclic glucans produced by the intramolecular transglycosylation activity of potato D-enzyme on amylopectin.
Potato D-enzyme catalyses an intramolecular transglycosylation reaction on amylose to produce cycloamylose, a novel cyclic alpha-1, 4 glucan. To determine if a similar activity could be observed with a high molecular weight branched substrate, recombinant potato D-enzyme was incubated with amylopectin. The substrate was converted into two fractions of lower molecular mass. Fraction I comprised 15% cyclic molecules of which the majority contained both alpha-1,4 and alpha-1,6 links. These were shown to be branched molecules with branches shorter than those in amylopectin. Fraction II comprised 80% cyclic molecules of which the majority contained only alpha-1,4 links (cycloamylose). Since fraction II appeared before fraction I, we propose that D-enzyme first catalysed the cyclisation of the outer side chains of amylopectin and then the cyclisation of inner chains to produce branched clusters. These results demonstrate that D-enzyme can catalyse the transfer of branched glucans, and suggest novel ways in which it may participate in starch metabolism in plants.
Takaha
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Institute of Cell and Molecular Biology, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh, EH9 3JH, United Kingdom. takaha-takeshi@glico.co.jp
Yanase
M
M
Takata
H
H
Okada
S
S
Smith
S M
SM
D000687:Amylopectin / Q000737:chemistry / Q000378:metabolism*; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism; D005936:Glucans / Q000096:biosynthesis* / Q000737:chemistry; D006004:Glycogen Debranching Enzyme System / Q000378:metabolism*; D006031:Glycosylation; D008954:Models, Biological; D008970:Molecular Weight; D010944:Plants / Q000378:metabolism; D011198:Solanum tuberosum / Q000201:enzymology; D013213:Starch / Q000378:metabolism
D005936:Glucans; D006004:Glycogen Debranching Enzyme System; D013213:Starch; D000687:Amylopectin; C020569:4 alpha-glucanotransferase; D005087:Glucan 1,4-alpha-Glucosidase