CYTOKININS AS INHIBITORS OF PLANT AMINE OXIDASE

The interaction of pea seedling amine oxidase with cytokinins was exam ined to probe a possible connection between cytokinin oxidase and amin e oxidase by determining whether cytokinins are substrates or inhibito rs of the latter. Kinetic measurements suggest that cytokinins are wea k competitive inhibitors of amine oxidase while their behaviour as sub strates was not observed. The absence of enzymatic activity with cytok inins as substrates denies the identity or even any similarity of thes e two enzymes which was previously considered [Hare, P.D. and van Stad en, J. (1994) J. Physiol. Plant., 91, 128]. From the values of the inh ibition constants obtained it seems unlikely that cytokinins take part in the regulation of amine oxidase activity in vivo. Their inhibitory effect on amine oxidase may be similar to that of some alkaloids stud ied earlier.