Further Studies on the Myofibrillar Adenosine Triphosphatase-Inhibitory Actitvity and the Mg++-dependent Adenosine Triphosphatase of the Relaxing Granules
1965 年 58 巻 5 号 p. 429-435
詳細
1965 年 58 巻 5 号 p. 429-435
1. Concentrated suspension of the relax-ing granules, which was capable of inhibiting myofibrillar ATPase, exhibited lower Mg++-dependent ATPase activity. The increasing dilution resulted in the increase of the ATPase activity concomitantly with the decrease of myofibrillar ATPase-inhibitory activity.
2. Two phases of the velocity, i.e., initial high velocity and subsequent stationary veloc-ity, could be distinguished when the time course of the Mg++-dependent ATPase was followed. The initial high velocity could be reduced by the increase of granular concentra-tion or completely eliminated by the addition of Ca++-binding agents. The addition of a small quantity of calcium caused an elevation of the initial high velocity.
3. The Mg++-dependent ATPase activity of the concentrated granules was scarcely affected by Ca++-binding agents.
4. The Mg++-dependent ATPase activity was enhanced about two folds by a low con-centration of calcium.
5. The action of Mg++-dependent ATPase always involves two phases, i.e., the Ca++-sensitive activity and the Ca++-insensitive activity as far as the reaction medium is not
perfectly free from calcium ion. GEDTA inhibits only the Ca++-sensitive activity of the ATPase.
6. The “stimulated” ATPase, obtainable by treating with desoxycholate, was greatly suppressed by GEDTA and EDTA.
The author wishes to express his sincerest thanks to Prof. Y. Akita of Tokyo University and Prof. M. Akino of Tokyo Metropolitan University for their guidance and criticism throughout this work. Thanks are also due to Assist. Prof. E. Ohnishi for his read-ing of the manuscript.
