On the active site of myosin A-adenosine triphosphatase IV. Properties of binding of trinitrobenzenesulfonate and p-chloromercuribenzoate to myosin a

The addition of ATP or PP_i retarded conspicuously the rate of specific binding of trinitrobenzenesulfonate to one mole of lysine residue in 2.1·10⁵ g of myosin A. The rate of specific binding of trinitrobenzenesulfonate to myosin A was increased in 4M LiBr which melts almost completely the helical structure of myosin A. The rate was also remarkably influenced by the treatment of myosin A with 1.5 M LiBr which inactivated ATPase (ATP phosphohydrolase, EC 3.6.1.3) without changing significantly the helical content of the myosin A molecule as a whole. Furthermore, it was demonstrated that actomyosin reconstituted from myosin A treated with p-chloromercuribenzoate and β-mercaptoethanol does not show a clearing response on addition of high concentrations of ATP and its ATPase activity is not inhibited by the substrate or by EDTA. The p-chloromercuribenzotae added was completely removed from myosin A by the further addition of excess β-mercaptoethanol and the optical rotatory dispersion of myosin A was insignificantly altered by the treatment with p-chloromercuribenzoate and β-mercaptoethanol.