Adenosine diphosphatase and adenosine triphosphatase activities of maize tonoplast‐enriched vesicles

Abstract

Microsomal fraction enriched with tonoplast vesicles was obtained from maize root (Zea mays L. FRB 73) by sucrose step gradient centri‐fugation. The vesicles contained an adenosine diphosphatase (ADPase) activity as determined by the hydrolysis of Mg‐ADP. The ADPase and adenosine triphospha‐tase (ATPase) of the fraction have different sensitivities toward several modifiers. ADPase activity was not sensitive to nitrate, N,N'‐dicyclohexylcarbodiimide (DCCD), diethylstilbestrol (DES), and azide, but partially sensitive to vanadate and molybdate. In contrast, ATPase was very sensitive to nitrate, DCCD, and DES, but not to vanadate, azide, and molybdate. The presence of 2'‐or (3')‐trinitrophenol adenosine 5'‐diphosphate (TNP‐ADP) significantly reduced ADPase activity but not that of the ATPase activity. On the other hand, the addition of TNP‐ATP abolished ATPase activity but not the ADPase activity. Since the influence of these modifiers to the activities are different, the binding and the hydrolysis of ADP and ATP in maize tonoplast vesicles may occur at different sites.

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An‐Fei Hsu

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