Some biochemical properties of cytokinin oxidase/dehydrogenase in Cucurbita pepo L. (zucchini) leaves

Cytokinin oxidase/dehydrogenase (CKX) was extracted and partially purified from intact leaves of Cucurbita pepo (zucchini) and its activity determined by an in vitro assay based on the measurement of the rate of conversion of [2-3H]iP to [2-3H] adenine. The optimum incubation time of the enzyme reaction under standard assay conditions was 3 h. Under these conditions the conversion of the substrate was almost linear and did not exceed 20%. The addition of copper-imidazole complex to the assay mixture resulted in a significant increase in the enzyme activity compared with the standard assay, especially during the first 6 h of incubation. The partially-purified enzyme extract exhibited a pH optimum at pH7.0-7.5 (Tris-HCl). The biochemical properties of zucchini enzyme preparations are discussed in view of the existing evidence for biochemical diversity of CKX.