固氮粪产碱菌谷氨酰胺合成酶的构象变化及调节作用

应用园二色谱测定了粪产碱菌（Ａｌｃａｌｉｇｅｎｅｓｆａｅｃａｌｉｓ）谷氨酰胺合成酶（ＧＳ）各构象，结果表明在Ｇｌｕ培养下α螺旋为２８％，β折叠为２２％，无规则卷曲占５０％；而在ＮＨ~＋_４培养下，三者相应为２０％，２０％，６０％。荧光光谱及付立叶红外光谱也证明，两种培养条件下ＧＳ的构象存在着差异。不同氮源对粪产碱菌ＧＳ的形成有显著的影响。高浓度ＮＨ~＋_４培养下ＧＳ合成受到阻遇，而Ｇｌｕ或低浓度ＮＨ~＋_４则对ＧＳ合成无明显的影响。ＮＨ~＋_４对固氮酶活性瞬间抑制可以被ＧＳ的抑制剂部分消除，但ＧＳ活性也受抑制。

The Conformation Status and Regulation of Glutamine Synthetase from Alcaligenes faecalis

The fluorescence emission spectra of GS from Alcaligenes faecalis (Af GS) and adenylylated Af GS (Af GS) are 337 nm and 340 nm, respectively. The variation indicated some difference of the stereo-structure between Af GS and Af GS. The CD spectra were also examined. The percentages of α-helix, β-sheet and random coil for Af GS and Af GS are 28, 22, 50 and 20, 20, 60, respectively. These data shwed that the secondary structure of Af GS and Af GS are different. These results were reconfirmed by FTIR assays. The effect of the nitrogen sources and its concentration on the synthesis and regulation of AfGS has been studied. The activity of GS is much higher in glutamate-grown cells than that in NH+4-grown cells, indicating that the Af GS biosynthesis is strongly depressed by high concentration of ammonia, and it is also highly adenylylated. However, this depression can be overcome by glutamate. MSX, a glutamine synthetase inhibitor, could partialy inhibit the nitrogenase activity, suggestign Af GS was involved in the regulation of nitrogenase activity in this bacterium.