Purification and regulatory properties of fructose 1,6-diphosphatase from Hydrogenomonas eutropha

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 Mg(2+) for activity. The MgCl(2) saturation curve was sigmoidal and the degree of positive cooperativity increased at lower fructose diphosphate concentrations. Mn(2+) can replace Mg(2+), but maximal activity was lower than that observed with Mg(2+) 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.