棕色固氮菌nifZ与固氮酶钼铁蛋白P-cluster合成的关系

Relationship Between nifZ and the Synthesis of P-cluster in Nitrogenase MoFe Protein of Azotobacter vinelandii

与野生型固氮菌（OP）MoFe蛋白相比，缺失nifZ的棕色固氮菌（AzotobactervinelandiiLipann）突变种的△nifZMoFe蛋白对乙炔的还原活性和Fe／Mo比值都显著降低。在相同实验条件下从这两种MoFe蛋白中抽提出的FeMoco在催化活性和金属组成方面都很相似，而这两种蛋白的圆二色（CD）谱则有显著差异，除在540－750nm外，△nifZMoFe蛋白在可见光区域380－540nm的△ε明显降低并在430nm附近处出现一个奇特的尖负峰；而在紫外区域的208nm和222nm负峰的高度却明显增加。△nifZMoFe蛋白可在合适浓度的PEG8000和MgCl2溶液中结晶出来，而晶体大小和出现沉淀多少与上述CD谱的负峰有关。这表明：棕色固氮菌nifZ与MoFe蛋白P-cluster的合成有关，并由此影响蛋白质的构象、稳定性和结晶过程。

In comparison with OP MoFe protein from wild type strain Azotobacter vinelandii Lipmann, the C2H2-reduction activity and atom ratio of Fe to Mo of △nifZ MoFe protein from a nifZ deletion strain of A. vivelandii were remarkably decreased. FeMoco, which were extracted from these two proteins under the samecondition, were almost s imilar to each other in activity and metal composition, and the circular dichroism (CD) Spectra of these proteins were significantly different from each other. In the visible region except 540 -750 nm, the △s at 380 ~ 540 nm of △nifZ MoFe protein decreased and had a peculiar sharp negative peak around 430 nm; and in the ultraviolet region, the peaks at 208 nm and 222 nm were higher than those of OP MoFe protein. △nifZ MoFe protein could be crystallized in a suitabe concentration of PEG 8000 and MgCl2, the size of crystals and amotmt of pmeipitation seemed to be related to the ab0Ve-mentioned negaive peaks. The results showed tha nng of Antobacter vinelandii might be related to the synthesis of P-cluster, rather than to that of FeMoco, which resulted in its conformation, stability and process of crystallization.