Abstract
The yield of S-1*** from tryptic digests of HMM was 65%. The s20, W value of S-1 was 5.03S at a concentration of 14.2 mg per ml. S-1 decomposed into smaller com-ponents at a rate of about 7% of total material per day in neutral salt solution at 0°C. A quarter as much degradation occurred on addition of 0.07M sucrose. The Ca2+-ATPase [EC 3. 6. 1. 3] activity of S-1 decreased in proportion to increase in the amount of smaller components. In 4.6-5M guanidine-HC1 and in alkaline (pH 11-11.5) solution, S-1 showed a broad sedimentation pattern with s20, w values of the peak of 1.1 and 1.5 S, respectively. The pattern of elution from Sephadex G-200 and G-100 showed that S-1 was degraded into small components in 5M guanidine-HCl or at pH 11.
The ratio of the ATPase activities of myosin (M. W. 4.8×105), HMM (3.4×105) and S-1 (1.2×105) on a molar basis was 1:1:0.5. This ratio was independent of the modifiers used. When myosin was subjected to carboxamidomethylation under the conditions where one specific cysteine residue was completely modified with IAA, the Ca2+ and Mg2+-ATPase activities of myosin increased 11.7 and 9.7 fold, respec-tively, but the EDTA-ATPase activity decreased by 76%. HMM and S-1 were pre-pared from this modified myosin. The extents of activation and inhibition of ATPase activities by IAA during their production of these fragments remained almost con-stant.
The amount of the initial stoichiometric burst of Pi-liberation per mole of S-1 was 0.55 to 0.6 mole, which was half of those of myosin and HMM. The rate of initial rapid Pi-liberation was independent of the ATP concentration when the latter was lower than 0.6 mole per mole of S-1, but at concentrations above this, it in-creased with increase in ATP concentration. The amount of initial rapid Pi-libera-tion increased linearly with the ATP concentration until the amount of added ATP reached about 0.6 mole per mole of S-1, and at higher ATP concentrations remained constant at this value.
