Clotrimazole对叶绿体ATPase功能的影响及其作用部位

Effect of Clotrimazole on the Function of Chloroplast Mg^(2+)-ATPase and Its Action Sites

clotrimazole能抑制 DTT+光激活的类囊体膜上Mg^(2+)—ATPase的活力。这种抑制属于可逆非竞争性抑制。进一步的实验还表明clotrimazole可以消除 9—AA光下荧光粹灭指示的正常类囊体及DCCD重组残缺膜的跨膜质子梯度。卵磷脂可以减缓 clotrimazole对9—AA荧光粹灭的抑制作用。clotrimazole还能抑制DTT加热激活的游离CF_1 Ca^(2+)—ATPase的活力。根据以上结果我们推测 clotrimazole在类囊体上可能有两个作用部位,一个在类囊体膜脂;另一个在CF_1。

Clotrimazole inhibited the Mg^(2+)-ATPase activity of thylakoids activatedby DTT+light. The degree of inhibi-tion was the same wether clotrimazolewas added at light activation stage or atdark reaction stage (Fig. 1). The re-sults indicated that clotrimazole inhibit-ed Mg^(2+)-ATPase activity of thylakoidsnon-competitively (Fig. 3). 9--AA flu-orescence quenching experimentsshowed that clotrimazole reduced theproton gradient across normal thy-lakoid membrane and the CF_1-depletedthylakoid membrane reconstituted withDCCD(Figs. 5 and 6). The effects ofclotrimazole on Mg^(2+)-ATPase and 9-AA fluorescence quenching were simi-lar to those of gramicidin D, an un-coupler known to act on the thylakoidmembrane lipids (Table 1, Fig. 6).Though the effects of clotrimazole onthe thylakoid Mg^(2+)-ATPase activitywere the same as those of DCCD (Fig.4), clotrimazole did not reconstitutewith CF_1-depleted thylakoids to restoreits 9-AA fluorescence quenching (Fig.5). The results imply that clotrimazolemight act on the thylakoid membranelipids as gramicidin D. When soybeanlecithin was present in the reactionmixture, clotrimazole and gramicidinD showed different effects on 9--AAfluorescence quenching (Fig. 6). Inaddition to that, clotrimazole could in-hibit the Ca^(2+)-ATPase activity of thesoluble CF_1 (Fig. 7). Basing on theabove results, we suggest that there beseveral action sites of clotrimazole onthe thylakoid, i. e., besides its actionsite on the electron transport chain likethat of DCMU (Wei et al. 1988),clotrimazole may also act on the thy-lakoid membrane lipids to increase pro-ton permeability and bind to CF_1, andthereby to affect chloroplast ATPaseactivity.