XVI International Botanical Congess
Cytokinin oxidase from corn kernels was purified, tryptic peptides were isolated and used to design primers for PCR. Subsequently, the cytokinin oxidase gene, ckx1, was cloned from a maize genomic library. It encodes a 60 KDa protein that possesses a signal peptide, eight glycosylation sequences, and a FAD-binding sequence. The gene contains FAD but does not contain copper or other metals. The kinetics were investigated using the native enzyme and the recombinant enzyme secreted by a Pichia pastoris culture expressing ckx1 cDNA. Both had similar substrate specificities, with a preference for isopentenyladenine and zeatin. The phenyl pyridylurea cytokinins were found to be effective competitive inhibitors of the oxidase.