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Purification and Regulatory Properties of Fructose 1,6-Diphosphatase from Hydrogenomonas eutropha

^a Institut für Mikrobiologie der Universität Göttingen, 3400 Göttingen, West Germany

ABSTRACT

Fructose diphosphatase of Hydrogenomonas eutropha H 16, produced during autotrophic growth, was purified 247-fold from extracts of cells. The molecular weight of the enzyme was estimated to be 170,000. The enzyme showed a pH optimum of 8.5 in both crude extracts and purified preparation. The shape of the pH curve was not changed in the presence of ethylenediaminetetraacetic acid. The enzyme required Mg²⁺ for activity. The MgCl₂ saturation curve was sigmoidal and the degree of positive cooperativity increased at lower fructose diphosphate concentrations. Mn²⁺ can replace Mg²⁺, but maximal activity was lower than that observed with Mg²⁺ and the optimal concentration range was narrow. The fructose diphosphate curve was also sigmoidal. The purified enzyme also hydrolyzed sedoheptulose diphosphate but at a much lower rate than fructose diphosphate. The enzyme was not inhibited by adenosine 5'-monophosphate but was inhibited by ribulose 5-phosphate and adenosine 5'-triphosphate. Adenosine 5'-triphosphate did not affect the degree of cooperativity among the sites for fructose diphosphate. The inhibition by adenosine 5'-triphosphate was mixed and by ribulose 5-phosphate was noncompetitive. An attempt was made to correlate the properties of fructose diphosphatase from H. eutropha with its physiological role during autotrophic growth.

¹ Present address: Department of Bacteriology, University of California, Davis, Calif. 95616.