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Metabolism and Enzymology

Isolation and Characterization of Phosphoenolpyruvate Phosphatase from Germinating Mung Beans (Vigna radiata) ¹

Department of Biochemistry, Faculty of Science, Banaras Hindu University, Varanasi-221 005, India

A phosphoenolpyruvate (PEP) phosphatase was purified to homogeneity from germinating mung beans (Vigna radiata). It was found to be a tetrameric protein (molecular mass 240,000 daltons) made up of apparently identical subunits (subunit molecular mass 60,000 daltons). It was free from bound nucleotides. It did not show pyruvate kinase activity. The enzyme showed high specificity for PEP. Pyrophosphate and some esters (nucleoside di- and triphosphates) were hydrolyzed slowly and phosphoric acid monoesters were not hydrolyzed. The enzyme showed maximum activity at pH 8.5. At this pH, the K_m of PEP was 0.14 millimolar and the V_max was equal to 1.05 micromoles pyruvate formed per minute per milligram enzyme protein. Dialysis of the enzyme against 10 millimolar triethanolamine buffer (pH 6.5), led to loss of the catalytic activity, which was restored on addition of Mg²⁺ ions (K_m = 0.12 millimolar). Other divalent metal ions inhibited the Mg²⁺ -activated enzyme. PEP-phosphatase was inhibited by ATP and several other metabolites.

¹ Financial assistance of the Council of Scientific and Industrial Research, New Delhi (Senior Research Fellowship to A. M. K.) is gratefully acknowledged. Part of this work was presented in an International Seminar on Structure and Function of Enzymes, held at Varanasi, India on October 22-25, 1986.