Catalytic Properties of Glucose-6-Phosphate Dehydrogenase from Pea Leaves

A. V. Semenikhina, T. N. Popova^*, and L. V. Matasova

Department of Plant Physiology and Biochemistry, Voronezh State University, Universitetskaya pl. 1, Voronezh, 394693 Russia; fax: (073) 78-9877; E-mail: root@bc.vsu.ru

^* To whom correspondence should be addressed.

Received August 19, 1998; Revision received March 15, 1999

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A homogeneous preparation of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) with a specific activity of 3.88 U/mg protein was isolated from pea (Pisum sativum L.) leaves. The molecular mass of the G6PDH is 79 ± 2 kD. According to SDS-PAGE, the molecular mass of the enzyme subunit is 40 ± 3 kD. The K_m values for glucose-6-phosphate and NADP are 2 and 0.5 mM, respectively. The enzyme has a pH optimum of 8.0. Mg²⁺, Mn²⁺, and Ca²⁺ activate the enzyme at concentrations above 1 mM. Galactose-6-phosphate and fructose-6-phosphate inhibit the G6PDH from pea leaves. Fructose-1,6-bisphosphate and galactose-1-phosphate are enzyme activators. NADPH is a competitive inhibitor of the G6PDH with respect to glucose-6-phosphate (K_i = 0.027 mM). ATP, ADP, AMP, UTP, NAD, and NADH have no effect on the activity of the enzyme.

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KEY WORDS: pea, glucose-6-phosphate dehydrogenase, purification, properties

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