(1→3)-β-d-Glucan Synthase from Sugar Beet

Abstract

A (1 .fwdarw. 3)-.beta.-glucan synthase has been isolated from petiole tissue of sugar beet (Beta vulgaris L.). Enzyme activity is associated with a membrane fraction with a density of 1.03 grams per cubic centimeter when subjected to isopycnic density grident centrifugation in Percoll. The reaction product was determined to be a linear (1 .fwdarw. 3)-.beta.-glucan by methylation analysis and by glucanase digestion. (1 .fwdarw. 3)-.beta.-Glucan synthase activity is markedly stimulated by Ca2+; activation is half-maximal at about 50 micromolar Ca2+ and is nearly saturated at 100 micromolar. Other divalent cations tested, Mg2+, Mn2+, and Sr2+, also stimulate enzyme activity but are less effective. Enzyme activity was also stimulated up to 12-fold by .beta.-glucosides. Siroflour, the fluorochrome from aniline blue, inhibited enzyme activity 95% when included at 1 millimolar. The enzyme was solubilized in Zwittergent 3-14;85% of total enzyme activity was solubilized in 0.03% detergent and the optimal detergent-to-protein ratio was 0.3 and 3 milligrams per milliliter protein.