d-Xylulokinase and d-Ribulokinase in Higher Plants

Abstract
D-Xululokinase occurs in tissues of higher plants, including pea seed, spinach leaf, wheat germ, and wheat seedling. The enzyme was obtained substantially free of xylose isomerase by fractionation with ammonium sulfate. Wheat germ x-xylulokinase showed optimal activity between pH 7.0 and 7.6. The enzyme from pea meal required divalent cations (Mg++. Mn++, or Co++) and sulfhydryl groups for maximum activity. Both D-xylulose and D-ribulose were phosphorylated, but D-xylose and D-ribose were not phosphorylated by the kinase.