Myosin and adenosinetriphosphatase

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Abstract
Myosin from skeletal and cardiac muscle broke down adenosinetriphosphate (ATP) to adenosinediphosphate (ADP). The action was activated by Ca++ and Mn++, much less by Ba++, Mg++ and Fe++. The most efficient activator was Ca++. Myosin. precipitated only once, contained an ADP-ase which was removed by further precipitations, and this enzyme was activated by Mn++ > Mg++ > Ca++. The enzymic activity of myosin was optimal at pH 9 and much greater in amino acid buffers then in bicarbonate. In glycine buffer at 37[degree], the activity unit Qp for rabbit myosin varied between 3000 and 6000, and decreased on storage of the protein. Qp values for other myosins were quoted. Purified myosln did not attack ADP, K diphenylpyro-phosphate or Na4P2O7. There was no apparent relation between enzyme activity and the ability to form sols showing flow birefringence. The ATP-ase of muscle differed in respect to its specificity and to the manner in which its activity was affected by Ca++ and Mg++ from the phosphatases of liver and electrical tissue. While it was possible to obtain myosin free from ATP-ase, it was not possible to obtain the enzyme unassociated with myosin, and none of the evidence was contrary to the view that myosin and ATP-ase were identical. Results were discussed in relation to the mechanism of muscle contraction.

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