Characterization of basic atpase of fragmented sarcoplasmic reticulum isolated from rabbit skeletal muscle
Yamada, S.; Fujii, J.; Inohara, N.
Reports of Faculty of Science Shizuoka University 21: 89-100
Incubation of sarcoplasmic reticulum (SR) with ethylene glycol bis(aminoethyl ether)-N,N,N'N',-tetraacetic acid (EGTA) followed inactivation of Ca-ATPase activity. But the EGTA did not inhibit basic ATPase activity. The characters of the basic ATPase were examined by using SR which was pretreated with EGTA to inactivate Ca-ATPase activity completely. The lineweaver-Burk plot of the basic ATPase activity showed two straight lines. Michaelis constants at high concentration range of ATP were 240 .mu.M and 280 .mu.M for MgATP and CaATP, respectively as substrates. The basic ATPase was activated in the presence of Mg2+, Ca2+, Mn2+ or Co2+. Apparent rate constants of basic ATPase activity increased in almost parallel with the concentration of MgATP, CaATP, MnATP or CoATP. This result suggests that MnATP and CoATP can be reacted by the enzyme as substrates as that MgATP and CaATP are reacted. But the activity was inhibited by Mn2+ or Co2+ at the high concentration range over 3 mM. Arrhenius plot of the basic ATPase activity showed a break at 28.4.degree.C for MgATP as substrate. The activation energies below and above the 28.4.degree.C are 13.5 kcal/mole and 6.9 kcal/mole, respectively for MgATP as substrate. The ATPAse activity for MgATP as substrate was influenced by PLP-modification, NaN3 and KCl. But the activity for CaATP as substrate was not influenced so much. These results suggest that some partial mechanism of the basic ATPase reaction for MgATP as substrate is different from that for CaATP as substrate, but both activities seem to be caused by the same enzyme.