Evidence for Ca²⁺ Regulated Magnesium ATPase of Thrombosthenin (Platelet Actomyosin)

Summary

The isolation of an actomyosin-like protein from platelets with a Ca²⁺ sensitive component is described. The addition of 1 mM EGTA results in approximately 40% and 75% inhibition of the Mg-ATPase activity depending on the mode of isolation. The inhibition can be released by a free Ca²⁺ concentration of 3×l0^-6 M. Superprecipitation is also inhibited by 1 mM EGTA and restored in the presence of 10^-5 M free Ca²⁺.

^* Present Address: Department of Neurology Mount Sinai School of Medicine of the City Univ. of New York Fifth Avenue and 100th street New York, New York 10029, U.S.A.

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