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Plant Physiology 79:114-117 (1985)
© 1985 American Society of Plant Biologists

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Articles

Hexose Kinases from the Plant Cytosolic Fraction of Soybean Nodules

Les Copeland and Matthew Morell1

Department of Agricultural Chemistry, University of Sydney, New South Wales 2006, Australia

The enzymes responsible for the phosphorylation of hexoses in the plant cytosolic fraction of soybean (Glycine max L. Merr cv Williams) nodules have been studied and a hexokinase (ATP:D-hexose 6-phosphotransferase EC 2.7.1.1) and fructokinase (ATP:D-fructose 6-phosphotransferase EC 2.7.1.4) shown to be involved. The plant cytosolic hexokinase had optimum activity from pH 8.2 to 8.9 and the enzyme displayed typical Michaelis-Menten kinetics. Hexokinase had a higher affinity for glucose (Km 0.075 millimolar) than fructose (Km 2.5 millimolar) and is likely to phosphorylate mainly glucose in vivo. The plant cytosolic fructokinase had a pH optimum of 8.2 and required K+ ions for maximum activity. The enzyme was specific for fructose (apparent Km 0.077 millimolar) but concentrations of fructose greater than 0.4 millimolar were inhibitory. The native molecular weight of fructokinase was 84,000 ± 5,000. The roles of these enzymes in the metabolism of glucose and fructose in the host cytoplasm of soybean nodules are discussed.

1 Recipient of an Alexander Hugh Thurburn Scholarship of the University of Sydney.




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Copyright © 1985 by the American Society of Plant Biologists