Pick U, Weiss M
Biochemistry Department, Weizmann Institute of Science, Rehovot, Israel.
Eur J Biochem. 1988 May 2;173(3):623-8. doi: 10.1111/j.1432-1033.1988.tb14044.x.
The early observation of light-dependent Ca-ATPase activity in chloroplast thylakoids [Avron, M. (1962) J. Biol. Chem. 237, 2011-2017] has been reinvestigated. It is demonstrated that in contrast to light-triggered Mg-ATP activity, Ca-ATPase activity is strictly dependent on delta microH+, the transthylakoid membrane electrochemical potential gradient, since (a) there is an absolute requirement for continuous illumination; (b) electron-transport mediators that catalyze proton uptake, like phenazinemethosulphate, methylviologen of ferricyanide, are essential and (c) uncouplers inhibit the activity. The Ca-ATPase activity is essentially unaffected by dithiols, but is inhibited by CF0-CF1 inhibitors including tentoxin, dicyclohexylcarbodiimide and antisera to CF1. Addition of Ca-ATP to thylakoids does not induce delta pH or delta psi (the electrical potential gradient) formation either in the light or following preillumination with dithiols, demonstrating that it is not coupled to proton translocation. It is also demonstrated that Ca-ATP or Ca-ADP does not induce a proton leak through CF0-CF1. It is concluded that the Ca-ATPase activity in chloroplast thylakoid reflects a partial reaction of ATP synthesis catalyzed by CF0-CF1, which is internally uncoupled from proton translocation but is dependent on energization by a transmembrane delta microH+.
叶绿体类囊体中光依赖性钙 - ATP酶活性的早期观察结果[阿夫龙，M.（1962年）《生物化学杂志》237卷，2011 - 2017页]已被重新研究。结果表明，与光触发的镁 - ATP活性相反，钙 - ATP酶活性严格依赖于δμH⁺，即类囊体膜电化学势梯度，原因如下：（a）绝对需要持续光照；（b）催化质子摄取的电子传递介质，如硫酸吩嗪甲酯、甲基紫精或铁氰化物，是必不可少的；（c）解偶联剂会抑制该活性。钙 - ATP酶活性基本上不受二硫醇的影响，但会被包括抗霉素A、二环己基碳二亚胺和CF1抗血清在内的CF0 - CF1抑制剂抑制。向类囊体中添加钙 - ATP在光照下或用二硫醇预照射后都不会诱导δpH或δψ（电势梯度）的形成，这表明它与质子转运不偶联。还表明钙 - ATP或钙 - ADP不会通过CF0 - CF1诱导质子泄漏。结论是，叶绿体类囊体中的钙 - ATP酶活性反映了由CF0 - CF1催化的ATP合成的部分反应，该反应在内部与质子转运解偶联，但依赖于跨膜δμH⁺的能量供应。
