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Articles

Phosphoenolpyruvate Carboxylase from Spinach Leaf Tissue

Inhibition by Sulfite Ion ¹

^a Department of Vegetable Crops, University of California, Davis, California 95616

Phosphoenolpyruvate carboxylase (EC 4.1.1.31), partially purified from spinach (Spinacia oleracea) leaves, is inhibited by SO₃^2– ion. The inhibition is competitive or mixed type with respect to HCO₃^– (Ki = 17 mM), and noncompetitive with respect to phosphoenolpyruvic acid (Ki = 11 mM), Mg²⁺ (Ki = 10 mM), and Mn²⁺ (Ki = 2.4 mM). The inhibitory effect of SO₃^2– is more significant in the presence of Mn²⁺ than in the presence of Mg²⁺. L-Malate, an inhibitor of phosphoenolpyruvate carboxylase activity, and SO₃^2– may bind at the same site on the enzyme. Glyoxal bisulfite and glyoxylate bisulfite are equally effective inhibitors of the enzyme activity as SO₃^2–, but -hydroxypyridinemethanesulfonate is a weak inhibitor. The data are discussed in relation to the physiological effect of the air pollutant (SO₂) on plant leaf metabolism.

¹ This work was supported by Research Grant R801338 from the United States Environmental Protection Agency.