The calmodulin-stimulated ATPase of maize coleoptiles forms a phosphorylated intermediate

The calmodulin-stimulated ATPase of maize coleoptiles is a 140,000 Mr polypeptide. In the present study, formation of a phosphorylated intermediate by the enzyme is demonstrated. Phosphorylation is sensitive to chasing with unlabelled ATP and to hydroxylamine; lanthanum enhances its intensity while calmodulin enhances phosphorylation in the presence of lanthanum but not in its absence. Ethyleneglycol-bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) inhibits phosphorylation of the purified enzyme, but microsome preparations give a band of phosphorylation of 153,000 Mr in its presence. This latter phosphorylated band was not abolished after a variety of permeabilising treatments in the presence of Triton X-100; phosphorylation of the enzyme was absent when sodium deoxycholate was used as the solubilising detergent. The identity of the 153,000 Mr band is discussed.