アカザラガイ横奮紋閉殻筋ミオシンの加熱による調節軽鎖の可逆的解離

抄録

Mg-ATPase of the striated adductor myosin of akazara scallop Chlamys nipponensis akazara was studied at various temperatures and calcium ion concentrations. At lower temperatures than 15°C, the myosin ATPase activit was totally sensitive to Ca²⁺. Above 20°C, however, the activity was increased at Ca²⁺ concentrations lower than 10^-6 M, resulting in the loss of Ca-sensitivity. This phenomenon was attributable to th edissociatoin of th eregulatory light chains from the myosin molecule during heat treatment. The dissociation rate and extent of the light chains were affected by several lfactors; the temperature and ionic strength mixture, th concentration of divalent cations such as Ca²⁺ and sr²⁺, and the concentration of F-actin. The heat-treated myosinwas able to regain its full content of regulatory light chain as well as its full Ca-sensitivity of the Mg-AATPase activity and of the superprecipitation ability of actomyosin. The heat treatment was demonstrated to be useful as a new device to desensitize akazara myosin, even in presence o th ephysiological concentration of Mg²⁺.