Properties of a high-affinity cytokinin-binding protein from wheat germ.

A soluble protein that interacts with a range of cytokinins was extensively purified from wheat (Triticum aestivum L.) germ. This protein has a K d for kinetin of 2×10(-7) M. The binding of kinetin to the protein is inhibited by low concentrations of synthetic and naturally-occurring cytokinins including N(6)-benzyladenine, N(6)-benzyladenosine, kinetin riboside, N(6)-dimethylallyladenine, N(6)-dimethylallyladenosine, zeatin, zeatin riboside, N(6)-dimethyladenine and N(6)-dimethyladenosine. Adenine, adenosine and several non-N(6)-substituted adenine derivatives were ineffective as inhibitors of kinetin binding. While N(6)-butyryl-3',5'-cyclic AMP, N(6),2-O'-dibutyryl-3',5'-cyclic AMP and 2',3'-cyclic AMP inhibited binding of kinetin to the protein, 3',5'-cyclic AMP was ineffective. The kinetin-binding protein is heat-labile and pronase-sensitive. Kinetin-binding activity exactly co-chromatographs with a single peak of carbohydrate and protein on gel-filtration and is displaced from concanavalin A-Sepharose 4B by α-methylglucoside. On gel filtration, the kinetin-binding protein behaves as a soluble protein with an apparent molecular weight of 180,000 daltons.