The effect of certain sulfur compounds on the myosin B-ATP system

1. 1. Exposure of myosin (B) ATPase to 0.01 − 0.001 M cysteine ethyl ester or S-β-aminoethylisothiuronium in mildly alkaline solution, followed by “washing out” of the sulfur compounds, converts the ATPase into a state wherein it is markedly more responsive to Ca ++ activation than protein not so treated. 2. 2. The v m (pH) relation of protein so treated resembles a simple titration curve, and, in particular, it appears to lose the velocity maximum at pH 6.4 which is characteristic of untreated protein. 3. 3. The intensity of light scattered from a freshly prepared dilution of myosin (B) decays markedly over the subsequent hours, as does the magnitude of the intensity drop evoked by ATP addition. The presence of 0.001 M S-β-aminoethylisothiuronium moderately accelerates these decays.