钼铁蛋白铁钼辅因子的有机组分对其功能的影响

棕色固氮菌(Azotobacter vinelandii)固氮酶的钼铁蛋白经邻菲啰啉在厌氧或有氧环境中处理后,变为 P-cluster 单一缺失或 P-cluster 和 FeMoco 同时缺失的失活钼铁蛋白。含柠檬酸盐或高柠檬酸盐的重组液都使这两种失活蛋白能恢复固氮酶重组的 H~ 和 C_2H_2还原活性,活性恢复程度随反映钼铁蛋白中金属原子簇含量变化的圆二色和磁圆二色谱及金属含量的恢复程度的提高而提高,但它们固 N_2能力的恢复程度则不相同:P-cluster 单一缺失的蛋白用两种重组液重组后均可恢复其固 N_2能力,而 P-cluster 和 FeMoco 同时缺失的蛋白,只有用含高柠檬酸盐的重组液重组才恢复其固 N_2能力,表明含不同有机组分的重组液所组装的 P-cluster 均与天然状态相同,只有含高柠檬酸盐的重组液所组装的 FeMoco 才与天然状态相同,从而证明高柠檬酸盐是 FeMoco 的必需的有机组分。

THE EFFECT OF THE ORGANIC COMPONENT OF FeMoco ON THE FUNCTION OF NITROGENASE MoFe PROTEIN

By treating the MoFe protein of nitrogenase from Azotobacter vinelandii with O-phenan- throline under anaerobic or aerobic condition,inactive MoFe protein which was partially de- ficient in P-cluster or in both P-cluster and FeMoco could be obtained.The above mentioned inactive MoFe proteins were incubated with a reconstituent solution containing Ma_2MoO_4,Na_2S, dithiothreitol(DTT)and homocitrate or citrate.Results showed that the acetylene and proton reduction activity of nitrogenase could be restored in both treated proteins after incubating with the reconstituent solution containing either citrate or homocitrate,and their metal content, CD and MCD spectra which reflected the content of metal clusters in the MoFe protein could also be restored.But their restoration of the N_2-reduction ability of the treated MoFe proteins was significantly different from each other,the P-cluster deficient MoFe protein could be res- tored by a reconstituent solution containing either citrate or homocitrate,and the P-cluster plus FeMoco deficient MoFe protein could only be restored by the reconstituent solution contain- ing homocitrate.The result indicated that the P-cluster assembled by the reconstituent solution containing either citrate or homocitrate was similar to that of the native MoFe protein,and the FeMoco which was assembled only by the reconstituent solution containing homocitrate was similar to that of the native MoFe protein.These results further demonstrated that homocitrate is an essential component of FeMoco.