Mg^(2+)对巯基修饰类囊体膜H^+-ATP酶的质子传导途径的调节效应

Regulatory Effect of Mg^(2+) on Proton Delivery Pathways of H^+-ATPase in Thiol-Modulated Thylakoids

镁离子为巯基修饰类囊体还原型H^+-ATP酶光活化所必需。介质中MgCl_2浓度由2mmol/L增加到10mmol/L时,解联剂NH_4Cl对H^+-ATP酶光活化的抑制作用明显减弱,而对跨膜⊿pH的消除效应并未减轻。介质中Mg^(2+)浓度的增加不影响DCMU对H^+-ATP酶光活化的抑制作用。 介质中含40μmol/LADP时,低浓度NH_4Cl对H^+-ATP酶催化的刺激效应被消除,仅呈现抑制作用。这种NH_4Cl对H^+-ATP酶催化活性的抑制作用随着反应介质中Mg^(2+)浓度的增加而降低,因此认为Mg^(2+)参与质子传导途径的调节。

Magnesium ions were required for light-activation of H^+-ATPase in thiol-modulated thylakoids (Fig. 1). The uncoupler NH_4Cl inhibited the activation of H^+-ATPase by a light lasting 10 s (Fig. 4). When the Mg^(2+)concentration in the activation mixture was raised from 2 mmol/L to 10 mmol/L, th inhibitory effect of NH_4Cl on the activation became weaker (Fig. 5), but there were little changes in either the dissipative effect of NH_4Cl on △pH across the membranes (Fig. 3) or the inhibitory effect of DCMU on the activation (Fig. 6). When 40 mmol/L ADP was present in the reaction medium, NH_4Cl did not stimulate but rather inhibited the catalysis by the activated H^+-ATPase (Fig. 7). This inhibitory effect of NH_4Cl on catalysis also varied with the Mg^(3+) concentration in the reaction medium (Fig. 8). The above results show that Mg^(2+) may be involved in the regulation of proton delivery pathways.