多粘菌素B对类囊体膜上M_g^(2+)-ATPase功能的影响及其作用部位

Effect of Polymyxin B on the Activity of Thylakoid Mg^(2+)-ATPase and Its Action Site on CF_1

多粘菌素B抑制类囊体膜上的Mg^(2+)-ATP酶活力,且其部分抑制作用受控于高能态。如将酶反应速度和[Mg^(2+)ATP]的浓度作双倒数图,则可观察到多粘菌素B和[Mg^(2+)ATP]浓度之间存在着类似竞争的关系。再经用多粘菌素B抑制游离的β亚单位的活力。证明多粘菌素B在偶联因子上的作用部位是在β亚单位上。

In the previous papers we had found that polymyxin B could increase the rate of photophosphorylation and P/O ratio and stimulate the ATP-Pi exchange reaction(Yin et al. 1979, Shen 1987). The present results showed that adding polymyxin B to the dark reaction mixture could inhibit the activity of thylakoid Mg^(2+)-ATPase activated by DTT+Light. The half maximal inhibition occurred at 30～40 μg/ml polymyxin B (Table 1, Fig. 1). The effect of polymyxin B on the ATP kinetics of the thylakoid Mg^(2+)-ATPase activated by DTT+Light was studied. The result was clear, with the lines for control and polymyxin B-inhibited one in double reciprocal plots crossing before the ordinate (Fig. 2). The results showed that polymyxin B was in some way competitivc with ATP. Mg^(2+). The results also showed that the partial inhibitory effect of polymyxin B on thylakoid Mg^(2+)-ATPase was dependent on the high energy state of thylakoid (Fig. 3, Table 3). Polymyxin B not only inhibited the activity of thylakoid Mg^(2+)-ATPase, but also the rate of Mg^(2+)-ATPase of purified β subunit from thylakoid coupling factors (Table 6). Besides the inhibition of thylakoid Mg^(2+)-ATPase activity, polymyxin B also inhibited thylakoid Mg^(2+)-GTPase activity (Table 4). The stimulatory effect of polymyxin B on soluble CF_1· Mg^(2+)-ATPase activated by methanol was observed (Table 5). From the above results we suggest that the action site of polymyxin B is on β subtmit of CF_1.