Partial Purification of Digitonin-Solubilized β-Glucan Synthase from Red Beet Root

An enriched glucan synthase fraction was obtained from red beet root microsomes by sequential extraction with the detergents 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and digitonin. The digitonin suspension was centrifuged on a glycerol gradient, where a glucan synthase peak with a specific activity of 30- to 40-fold over microsomes was recovered. Most protein contaminants were found in the gradient pellet. The glucan synthase-containing fraction was largely free of plasma membrane and tonoplast-derived ATPase activity and was enriched with a protein subunit of 68 kilodaltons.