高柠檬酸盐对固氮酶铁钼辅基重组活性的影响

Effect of Homocitrate on Reconstitution Activity of FeMoco from Nitrogenase

用高柠檬酸铁、柠檬酸钠、ＡＴＰ和Ｎａ２ＭｏＯ４分别处理ＦｅＭｏｃｏ，然后与ＵＷ４５组份Ⅰ蛋白进行重组，结果发现，高柠檬铁和柠檬酸钠分别使ＦｅＭｏｃｏ重组体的Ｃ２Ｈ２还原活性提高６７％和５４％，Ｎ２还原活性分别提高１７０％和１３５％．ＦｅＭｏｃｏ与ＡＴＰ预作用后再分别与高柠檬酸铁、柠檬酸钠作用，其重组体的Ｃ２Ｈ２还原活性分别提高１２１％和１１９％，而Ｎ２还原活性分别提高３０３％和１３５％．而ＦｅＭｏｃｏ，ＦｅＭｏｃｏ－高柠檬酸铁体系及ＦｅＭｏｃｏ－ＡＴＰ－高柠檬酸铁体系与Ｎａ２ＭｏＯ４作用后，重组体的Ｃ２Ｈ２还原活性分别下降５％，１２％及２１％．ＦｅＭｏｃｏ－高柠檬酸铁体系在１４．６Ｋ下的ＥＰＲ谱，与单独ＦｅＭｏｃｏ的略有不同，而ＦｅＭｏｃｏ－ＡＴＰ－高柠檬酸铁体系的ＥＰＲ谱则与前者有明显的差异．研究结果表明，高柠檬酸可能是ＦｅＭｏｃｏ的有机组份，它可能结合在ＦｅＭｏｃｏ的Ｍｏ原子上，而这种结合是比较松散的．

Reconstitution activities of FeMoco treated with a series of substances were inverstigated. It was found that homocitrate and citrate could significantly enhance the reconstitution activety of FeMoco. The C2H2-reduction activity increased by 67%/54% and N2-reduction activity increased by 170 % /135%, respectively, when FeMoco incubated with homocitrate/citrate before reconstitution with UW45 component I protein. If FeMoco incubated with ATP and then with homocitrate/citrate, the C2H2-reduction activity increased by 121 %/119% and N2-reduction activity increased by 303%/135%, respectively. When FeMoco, FeMoco-homocitrate and FeMoco-ATP-homocitrate were treated with Na2MoO4, the C2H2-reduction activity decreased by 5%, 12% and 21 %, respectively. The characteristics of EPR spectrum of FeMocoATP-homocitrate was significantly different from that of FeMoco or FeMoco-homocitrate system at 14. 6 K. The results suggested that homocitrate is an organic composition of FeMoco and it is probably that homocitrate is loosely linked with Mo in FeMoco. ATP is probably linked with Fe in FeMoco and facilitate the combination between FeMoco and homocitrate.