ADENOSINE DIPHOSPHATASE AND ADENOSINE-TRIPHOSPHATASE ACTIVITIES OF MAIZE TONOPLAST-ENRICHED VESICLES

Microsomal fraction enriched with tonoplast vesicles was obtained from maize root (Zea mays L. FRB 73) by sucrose step gradient centrifugati on. The vesicles contained an adenosine diphosphatase (ADPase) activit y as determined by the hydrolysis of Mg-ADP. The ADPase and adenosine triphosphatase (ATPase) of the fraction have different sensitivities t oward several modifiers. ADPase activity was not sensitive to nitrate, N,N'-dicyclohexylcarbodiimide (DCCD), diethylstilbestrol (DES), and a zide, but partially sensitive to vanadate and molybdate. In contrast, ATPase was very sensitive to nitrate, DCCD, and DES, but not to vanada te, azide, and molybdate. The presence of 2'-or (3')-trinitrophenol ad enosine 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. Sinc e the influence of these modifiers to the activities are different, th e binding and the hydrolysis of ADP and ATP in maize tonoplast vesicle s may occur at different sites.