van de Put F H, Visser G J, Donkers E A, Theuvenet A P, Willems P H
Department of Biochemistry, University of Nijmegen, The Netherlands.
Eur J Biochem. 1993 Dec 15;218(3):959-62. doi: 10.1111/j.1432-1033.1993.tb18453.x.
The potent inhibitor of Ca2+, Mg(2+)-ATPase activity, thapsigargin, has been used to investigate the effect of ambient free Ca2+ on basal Mg(2+)-dependent ATPase activity in rat liver microsomes. Thapsigargin non-competitively inhibited both Ca(2+)-stimulated ATP-dependent Ca2+ uptake and Ca(2+)-stimulated Mg(2+)-dependent ATPase activity. At a concentration of 1 microM, thapsigargin completely inhibited the Ca(2+)-pump activity, without affecting Mg(2+)-dependent ATPase activity measured in the absence of Ca2+. Increasing the ambient free Ca2+ concentration did not alter the basal Mg(2+)-dependent ATPase activity. The data presented indicate that ATPase activity measured in the absence of Ca2+ is a reliable measure for the basal Mg(2+)-dependent ATPase activity and that, consequently, the Ca(2+)-stimulated Mg(2+)-dependent ATPase activity can indeed be defined as the difference between the ATPase activity measured in the presence and the absence of Ca2+.
钙离子、镁离子 -ATP酶活性的强效抑制剂毒胡萝卜素，已被用于研究细胞外游离钙离子对大鼠肝微粒体中基础镁离子依赖性ATP酶活性的影响。毒胡萝卜素非竞争性地抑制了钙离子刺激的ATP依赖性钙离子摄取以及钙离子刺激的镁离子依赖性ATP酶活性。在浓度为1微摩尔时，毒胡萝卜素完全抑制了钙离子泵活性，而不影响在无钙离子情况下测得的镁离子依赖性ATP酶活性。提高细胞外游离钙离子浓度并未改变基础镁离子依赖性ATP酶活性。所呈现的数据表明，在无钙离子情况下测得的ATP酶活性是基础镁离子依赖性ATP酶活性的可靠指标，因此，钙离子刺激的镁离子依赖性ATP酶活性确实可以定义为在有钙离子和无钙离子情况下测得的ATP酶活性之差。
