Cytokinin Oxidase from Wheat

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Abstract
As part of the study of the possible role(s) of CBF-1, a cytokinin-binding protein abundant in wheat embryo, a cytokinin oxidase was found in wheat (Triticum aestivum L.) germ and partially purified by conventional purification techniques and high performance chromatofocusing. This preparation catalyzes conversion of N6-(.DELTA.2-isopentenyl)adenosine to adenosine at a Vmax of 0.4 nanomol per milligram protein per minute at 30.degree.C and pH 7.5, the Km binding 0.3 micromolar. This high affinity and the apparent molecular weight of 40,000 estimated by high performance gel permeation on a Spherogel TSK-3000 SW column indicate that this enzyme is different from cytokinin oxidases previously reported. Oxygen is required for the reaction, as for other cytokinin oxidases already described. N6-(.DELTA.2-isopentenyl)adenosine-5''-monophosphatase is apparently not a substrate. Benzyladenine is degraded, but to a small extent, and it inhibits slightly the degradation of N6-(.DELTA.2-isopentenyl)adenosine. The degradation of N6-(.DELTA.2-isopentenyl)adenosine is strongly inhibited by diphenylurea and its highly active derivative N-(2-chloro-4-pyridyl)-N''-phenylurea.