A theoretical study on the regulation mechanism of Ca2+ concentration in lens related to the Ca2+ dependence of Ca2 (+) -ATPase activity
Imaizumi, M.; Furushima, M.; Nakatsuka, K.; Yamanouchi, U.
Nippon Ganka Gakkai Zasshi 94(2): 135-140
1990
ISSN/ISBN: 0029-0203 PMID: 2142377 Document Number: 353632
A four-state model for the elementary process of the Ca2+ active transport system in lens was proposed, and based upon this model the Ca2+ dependence of Ca2(+)-ATPase activity was analyzed. The results indicated that the Ca2(+)-ATPase activity reaches a peak at approximately pCa 4-5, and decreases at higher and lower Ca2+ concentrations. In the range of pCa 5-6, ATPase activity increases with Ca2+ concentration. Therefore, the model accounts for the kinetic properties of Ca2(+)-ATPase is a qualitative way. Moreover, it is proved that the Ca2+ dependence of Ca2(+)-ATPase activity is theoretically based upon the changes in Ca2+ affinity of Ca2+ binding sites and the Ca2+ dependence of Ca2(+)-ATPase activity is possibly involved in the regulation of intracellular Ca2+ concentration in vivo as a switching mechanism.