Abstract
The inactivation of myosin A-ATPase proceeds according to the first-order law. The rate constants of the inactivation were proportional to the 1.3, 0, and −3.3 powers of [H +], respectively, in the ranges of pH 5.2–6.0, 7.5–8.5, and 10.0–10.5. In these three ranges of pH, Δ H‡ values were 31.6, 52.6, and 42.1 kcal./mole, respectively. During the incubation at 36 °C. the α component in chromatographic profiles on diethylaminoethylcellulose decreased, the β component increased, and finally the β component decomposed. However, specific ATPase activities of both the α and the β components were not constant and decreased with time. Under three conditions (pH 7.0 and 30 °C., pH 5.7 and 20 °C., and pH 10.3 and 20 °C.), the change in optical rotatory dispersion with time was measured and compared with that of ATPase activity. The helical content decreased very slowly and only by a few per cent, even after ATPase activity disappeared.
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