Hydrogenase is a key enzyme for a coming hydrogen energy society, because it has strong catalytic activities on both uptake and production of dihydrogen. We, however, have to overcome the sensitivity against O₂ of the enzyme, because hydrogenase is, generally, easily inactivated in the presence of O₂. In this study, we have revisited the crystal structures of [NiFe]‑hydrogenase from sulfate-reducing bacterium in the several oxidized and reduced conditions. Our results revealed that the Ni‐Fe active site of the enzyme exposed into O₂ showed two forms, Form-1 and Form-2. The Ni‐Fe active site in Form-1 showed the typical Ni‐B (inactive ready) structure, whereas those in Form-2 lost Ni with no relation to an exposure time to O₂, and two cysteinyl sulfur ligands made a disulfide bond. On the other hand, the formation of sulfenylation of the cysteinyl ligand to Ni, which is often observed in the oxidized form, did not correlate with the Ni-elimination, but with exposure time to O₂.

氢酶是即将到来的氢能社会的关键酶，因为它对二氢的吸收和产生均具有很强的催化活性。但是，我们必须克服对酶O ₂的敏感性，因为氢化酶通常在O ₂存在下很容易失活。在这项研究中，我们已经重新研究了硫酸盐还原细菌在几种氧化和还原条件下的[NiFe]-加氢酶的晶体结构。我们的结果表明，暴露于O ₂的酶的Ni-Fe活性位点表现出两种形式，即形式1和形式2。晶型1中的Ni-Fe活性位点显示出典型的Ni-B（惰性准备就绪）结构，而晶型2中的Ni-Fe活性位点损失了Ni，与O ₂的暴露时间无关，两个半胱氨酰硫配体形成一个二硫键。另一方面，通常以氧化形式观察到的半胱氨酰配体的亚磺酰基化成Ni，与消除Ni无关，但与暴露于O _2的时间无关。