Hydrolysis of Nucleoside Di- and Tri-phosphates by Alkaline Inorganic Pyrophosphatases of Rat Liver and Yeast

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Abstract
Alkaline inorganic pyrophosphatases [EC 3.6.1.1] from various sources are known to hydrolyze nucleoside polyphosphates in addition to PP1. From our results we concluded that hydrolyses of both PP1 and nucleoside triphosphates by rat liver PP1ases preparations were catalyzed by a single enzyme protein, because (1) on column chromatographies on Sephadex G-100 and DEAE Sephadex A-50 and electrophoresis on polyacrylamide gel maximal activities towards PP1 and ITP always coincided and (2) in the presence of both PP1 and ITP as substrates, the amount of P1 liberated was less than the sum of the amounts liberated from PP1 and ITP separately. We also found that rat liver PP1ases were quite different from yeast PP1ase with respect to hydrolysis of ITP. With rat liver PP1ases in the presence of Mg2+, IMP was the end product with little accumulation of IDP as the intermediate, while with Yeast enzyme under similar conditions in the presence of Zn2+, IDP accumulated first before IMP was formed.

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