Characterization of specific binding sites for a mitogenic sulfated peptide, phytosulfokine‐α, in the plasma‐membrane fraction derived from Oryza sativa L.

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Abstract
Treatment of rice cells with an endogenous mitogenic peptide, phytosulfokine-α (PSK-α), results in cell proliferation. In the present study, [3H]PSK-α prepared by catalytic reduction of a PSK-α analog containing tetradehydroisoleucine was employed to identify putative PSK-α target molecules on rice plasma membranes. Membrane binding of the ligand was found to be saturable, reversible and pH dependent. Scatchard analysis demonstrated the existence of both high- and low-affinity binding sites with Kd values of 1.4 nm and 27 nm, respectively. Competition studies with [3H]PSK-α and several PSK-α analogs showed that displacing activity closely corresponds to the ability to induce cell proliferation. The properties of the binding sites distributed on plasma membranes are consistent with the function of PSK-α receptors in activating a cascade of molecular events involved in plant cell proliferation.