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Auxin Receptors of Maize Coleoptile Membranes Do Not Have ATPase Activity ¹

Ulrike C. Dohrmann² and Peter M. Ray

Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305, Department of Biological Sciences, Stanford University, Stanford, California 94305

Membrane-localized auxin-binding sites from coleoptiles and primary leaves of Zea mays L. which may be auxin receptors can be fully solubilized by 1 to 1.5 mg of Triton X-100 per mg of membrane protein (about 1 mg per gram of original tissue fresh weight), while 70% of the basal (Mg²⁺)-ATPase and 85% of the K⁺-stimulated (Mg²⁺)-ATPase (pH 6) remain pelletable. Gel exclusion chromatography on Bio-Gel A-1.5m indicates that the solubilized receptors occur as detergent-protein micelles of about 90,000 daltons equivalent molecular weight. Solubilized ATPase activities occur (a) as very large particles excluded from the gel, and (b) as particles of a size substantially smaller than the particles that exhibit auxin binding. The auxin-binding receptor therefore appears not to be an ATPase.

¹ This work was supported by a Carnegie Institution of Washington fellowship to J. W. C., and by grants from the National Science Foundation and the Research Development Fund of Stanford University to P. M. R. C.I.W.-D.P.B. publication No. 604.