镁、钙离子对组装于人工膜上CF_0-CF_1质子传导的影响

The Effect of Mg^(2+) or Ca^(2+) on Proton-conduction of CF_0-CF_1 Reconstituted into Planar Bilayer

在电压籍位下，研究Mg2+、Ca2+对重组于平板脂双层上CF0－CF1质子传导的影响，表明：（1）跨膜质子梯度为0时（△pH=0），在30～150mV范围内，Ca2+引起的正电流比在无金属离子溶液中有一定幅度的增加。在50mV以上，Mg2+比Ca2+有更大的促进正向电流的作用；（2）当△pH=3时，Mg2+比Ca2+更有显著增加正向膜电流的作用，电压在0mV时就已显示出来；（3）Ca2+不影响Mg2+促进正向电流的作用；（4）当△pH=3时，Ca2+”溶液中DTT促进正向电流的作用要在30mV以上才能显示，并随电位的增加而增大。而Mg2+溶液中，△pH=3，电压为0mV时DTT促进正向电流的作用就能显示出来，且在0至150mV范围内促进的幅度是恒定的。这就说明Mg2+不仅具有调节CF0－CF1质子传导的作用，而且也有助于膜结合CF0-CF1的变构，引起埋于CF0-CF1内部的γ亚单位二硫键暴露出来，促使二硫键为DTT还原，从而增加质子传导量。当CA2+、Mg2+存时，Ca2+不影响Mg2+的作用效应，它仅因其静电屏蔽效应稳定H+．-ATP酶的构象，从而促进对质子的传导。

Chloroplast ATP synthesis(CF0-CF1 ) is key enzyme for energy conversion. In recent years, functional assemble and analysis of H+ channelformed by CF0-CF1 on the lipid bilayerhave aroused wide interest.In this work, we studied the effectsof Mg2+ or Ca2+ on proton conductionthrough CF0-CF1 reconstituted into aplannar lipid bilayer under voltage-clampmede. The results obtained were as follow:(1 ) When the transmembrane(BLMs) proton gradient was zero (pH =0), the posihve membrane current whichwould increase with holding potential(HP) from 0 to 150 mV and a magnitudeof stimulation by Ca2+ from 0 to 150 mVat a constant rate. However, in caseMg2+ substituted for Ca2+ the membranecurrent showed a pronounced increasewhen the holding potential was higherthan 50 mV.(2) When transmembrane protongradient maintained at 3 (pH = 3) underholding potential at zero, the stimulationof membrane current by Mg2+ was manifested. However, stimulation of membrane current by Ca2+ took place at afterholding potential higher than 30 mV andthe magntitude of stimulation by Ca2 + wasless than that of the Mg2+.(3) Ca2+ had no effect on the stimulation of membrane current by Mg2+.(4) When Mg2+ was present, themagnitude of stimulation of membranecurrent increased by dimiotaitol (DTT)with the holding potential changing fromzero to 150 mV remained constant in thepresence of Ca2 +, me stimulated of themembrean current when the holding potential was higher than 30 mV.These results show that the Mg2+not only regtilates proton conductance ofCF0-CF1 but also is favors the inductionof conformation chang in membrane-bound CF0-CF1 and cause the γ-subunit hidden in CF0-CF1 to come to the surfaceand disulfide bond in it to be reduced byDTT, thus increasing the amount of proton conduction. Owing to the action asan electrostatic shield of Ca2+ was favorable for the stabilization of the conformation of CF0-CF1, it increases the membrane current.