Evidence for a Hexosediphosphatase from the Cytoplasm of Spinach Leaves

Latzko, Erwin; Zimmermann, Gerhard; Feller, Urs (1974). Evidence for a Hexosediphosphatase from the Cytoplasm of Spinach Leaves. Hoppe-Seyler's Zeitschrift für physiologische Chemie, 355(3), pp. 321-326. De Gruyter 10.1515/bchm2.1974.355.1.321

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Two peaks of hexosediphosphatase activity could be separated from spinach leaves by DEAE-Sephadex chromatography. Since extracts of isolated intact chloroplasts exhibited only one peak of enzyme activity we conclude that spinach leaves contain two hexosediphosphatases, one in the chloroplasts and one in the cytoplasm. Purified hexosediphosphatase prepared according to Racker and Schroeder and Buchanan et al. contained only the chloroplast enzyme.
Both enzymes catalyse specifically the hydrolysis of fructose 1,6-bisphosphate to fructose 6-phosphate and inorganic phosphate and show an absolute requirement for Mg2®. The concentration·, of Mg2® has no effect on the pH-optimum of the. cytoplasmic enzyme.
The cytoplasmic hexosediphosphatase differs from the chloroplast enzyme in the following properties: assayed with 10 mM Mg2® the pH optimum is lower, (7.5 for the cytoplasmic and 8.5 for the chloroplast enzyme) and the affinity for fructose bisphosphate at the pH optimum is greater.
In contrast to the chloroplast enzyme, the cytoplasmic enzyme is not activated by dithiothreitol or cystamine, but is inhibited by adenosine 5'-phosphate.

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