Purification and Properties of Potato: α‐1,4‐Glucan 6‐Glycosyltransferase (Q‐Enzyme)

George S. Drummond, Eric E. Smith, William J. Whelan

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30 Scopus citations


Potato Q‐enzyme (α‐1,4‐glucan: α‐1,4‐glucan 6‐glycosyltransferase) has been purified at least 430‐fold. Its instability in the purified state was reversed by Cleland's reagent (dithiothreitol) and the preparation was essentially free of other starch‐metabolising enzymes (β‐amylase, β‐glucosidase, D‐enzyme and R‐enzyme). Studies involving successive and simultaneous actions of Q‐enzyme and pullulanase on amylose showed that the final average unit‐chain length and iodine stain of the products were almost identical, but gel filtration revealed that their chain‐length distributions were different. Similarly, two amylopectin‐like polysaccharides formed by the direct action of Q‐enzyme on amylose and by the combined action of Q‐enzyme and potato phosphorylase on glucose 1‐phosphate were debranched with pullulanase and their unit‐chain length distributions compared by gel filtration with that of a debranched native amylopectin. In neither case was the unit‐chain profile of native amylopectin reproduced. The Q‐enzyme preparation has been shown to introduce additional branch points into amylopectin with the formation of a significant proportion of maltohexaosyl side chains. Evidence is presented that Q‐enzyme and not a second branching enzyme is responsible for this action and a mechanism for the formation of the maltohexaosyl chains is proposed.

Original languageEnglish (US)
Pages (from-to)168-176
Number of pages9
JournalEuropean Journal of Biochemistry
Issue number2
StatePublished - Mar 1972

ASJC Scopus subject areas

  • Biochemistry


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