Abstract

Calcium dependence of the Mg-ATPase activity and calcium binding of three myosins was investigated: akazara striated adductor myosin and its hybrid myosins with 20 kd-light chains of chicken gizzard myosin and with DTNB-light chains of rabbit skeletal myosin. All the three myosins bound two moles of Ca2+ per mole of myosin. One mole of Ca-binding was inhibited by Mg2+ in akazara myosin and the hybrid myosin with the 20 kd-light chains, both myosins whose Mg-ATPase activity showed Ca-sensitivity. On the other hand, two moles of Ca-bindings were inhibited by Mg2+ in the hybrid myosin with DTNB-light chains, the myosin whose Mg-ATPase activity showed no Ca-sensitivity. Desensitized akazara myosin did not bind Ca2+.

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