Glycogen biosynthesis in Chromatium strain D II. Purification and properties of glycogen synthetase

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Glycogen synthetase, ADP-glucose-a (1→4) glucan transglucosylase [E.C. 2.4.1.11] from a purple sulfur bacterium, Chromatium, was purified to a homogeneous state and its enzymic properties were studied. The molecular weight of the enzyme was 8.6 × 10^4 dalton as determined by analytical gel filtration on a column of Sephadex G-100. Since sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave the molecular weight value of 8.4 × 10^4 to the monomeric form of the enzyme, we concluded that Chromatium glycogen synthetase is comprised of a single polypeptide chain. The optimal pH of the transglucosylation reaction was between 8.0-8.5. The enzyme molecule utilized only ADP-glucose as the glucose donor. The Km value was determined as 3.8 ×10^<-4> M by the radioisotopic method of measuring the incorporation of ^<14>C-glucose into the acceptor glycogen, and 6.1 × 10^<-5> M by the enzyme coupling method. The most effective glucose acceptor (primer) was proved to be a long-chain a (1→6) branched a (1→4) polyglucan, e.g. Chromatiun and cow glycogen, whereas short-chain malto-oligosaccharides were much less efficient in the chain-elongation reaction.
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