Walker C C, Yates M G
Biochimie. 1978;60(3):225-31. doi: 10.1016/s0300-9084(78)80818-9.
H2 will support nitrogenase activity (C2H2 reduction) in Azotobacter chroococcum with or without added carbon substrate. Results show that H2 is metabolised to transfer electrons to nitrogenase and to the respiratory chain to produce ATP. H2-supported nitrogenase activity is most significant at low carbon substrate concentrations, but also occurs at saturating concentration. Continuous cultures of N2-fixing A. chroococcum evolved H2 from nitrogenase under O2-N2- and C-limited conditions. This H2 represented a significant proportion of nitrogenase activity. Hydrogenase activity was consistently high under C-limited conditions, but low or undetectable under O2- and N2-limitations. Pre-treatment with 40 per cent C2H2 inhibited hydrogenase activity in C-limited cultures, and H2 evolution increased under air and under Ar:O2 (4:1) mixtures. We deduce that hydrogenase : I, recycles H2 produced by nitrogenase to provide electrons and energy for N2 reduction: II, supports respiratory protection for nitrogenase under C-limited conditions, and III, does not act to prevent any inhibition of N2 reduction by H2 produced by nitrogenase. A scheme for the H2 cycle in N2-fixing A. chroococcum is proposed.
无论是否添加碳底物，氢气（H₂）都能支持褐球固氮菌中的固氮酶活性（乙炔还原）。结果表明，H₂被代谢以将电子传递给固氮酶和呼吸链来产生ATP。在低碳底物浓度下，H₂支持的固氮酶活性最为显著，但在饱和浓度下也会发生。在氧气、氮气和碳受限条件下，固氮的褐球固氮菌连续培养物从固氮酶中释放出H₂。这种H₂占固氮酶活性的很大一部分。在碳受限条件下，氢化酶活性始终很高，但在氧气和氮气受限条件下较低或无法检测到。用40%的乙炔预处理会抑制碳受限培养物中的氢化酶活性，并且在空气和氩气：氧气（4:1）混合物中H₂的释放增加。我们推断，氢化酶：I，回收固氮酶产生的H₂以为氮气还原提供电子和能量；II，在碳受限条件下为固氮酶提供呼吸保护；III，不会阻止固氮酶产生的H₂对氮气还原的任何抑制作用。提出了固氮的褐球固氮菌中H₂循环的示意图。
