Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Phosphorylated alpha (1right-arrow 4)Glucans as Substrate for Potato Starch-Branching Enzyme I1

Anders Viksø-Nielsen*, Andreas Blennow, Tom Hamborg Nielsen, and Birger Lindberg Møller

Plant Biochemistry Laboratory, Department of Plant Biology, Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark

The possible involvement of potato (Solanum tuberosum L.) starch-branching enzyme I (PSBE-I) in the in vivo synthesis of phosphorylated amylopectin was investigated in in vitro experiments with isolated PSBE-I using 33P-labeled phosphorylated and 3H end-labeled nonphosphorylated alpha (1right-arrow4)glucans as the substrates. From these radiolabeled substrates PSBE-I was shown to catalyze the formation of dual-labeled (3H/33P) phosphorylated branched polysaccharides with an average degree of polymerization of 80 to 85. The relatively high molecular mass indicated that the product was the result of multiple chain-transfer reactions. The presence of alpha (1right-arrow6) branch points was documented by isoamylase treatment and anion-exchange chromatography. Although the initial steps of the in vivo mechanism responsible for phosphorylation of potato starch remains elusive, the present study demonstrates that the enzyme machinery available in potato has the ability to incorporate phosphorylated alpha (1right-arrow4)glucans into neutral polysaccharides in an interchain catalytic reaction. Potato mini tubers synthesized phosphorylated starch from exogenously supplied 33PO43- and [U-14C]Glc at rates 4 times higher than those previously obtained using tubers from fully grown potato plants. This system was more reproducible compared with soil-grown tubers and was therefore used for preparation of 33P-labeled phosphorylated alpha (1right-arrow4)glucan chains.

1   This work was financially supported by the European Union Fishery and Agiculture Industrial Research program and by the Danish Food Technology Program (Føtek II).
*   Corresponding author; e-mail avn{at}kvl.dk; fax 45-35-28-33-33.

Plant Physiol. (1998) 117: 869-875
Copyright Clearance Center:   0032-0889/98/117/0869/07
© 1998 American Society of Plant Physiologists




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