Boison G, Schmitz O, Mikheeva L, Shestakov S, Bothe H
Botanisches Institut, Universität zu Köln, Cologne, Germany.
FEBS Lett. 1996 Sep 30;394(2):153-8. doi: 10.1016/0014-5793(96)00936-2.
Among cyanobacteria, the heterocystous, N2-fixing Anabaena variabilis and the unicellular Anacystis nidulans have recently been shown to possess an NAD+-dependent, bidirectional hydrogenase. A 5.0 kb DNA segment of the A. nidulans genome is now identified to harbor the structural genes hoxUYH coding for three subunits of the bidirectional hydrogenase. The gene arrangement in A. nidulans and in A. variabilis is remarkably dissimilar. In A. nidulans, but not in A. variabilis, the four accessory genes hoxW, hypA, hypB and hypF could be identified downstream of hoxH. An insertional homozygous mutant in hoxH from A. nidulans was completely inactive in performing Na2S204-dependent H2 evolution but could utilize the gas with almost 50% of the activity of the wild type. These findings with the first defined hydrogenase mutant in any photosynthetic, 02-evolving microorganism indicate that the unicellular cyanobacterium A. nidulans possesses both an uptake and a bidirectional hydrogenase. The physiological role(s) of the two hydrogenases in unicellular non-N2-fixing cyanobacteria is not yet understood.
在蓝细菌中，异形胞、固氮的多变鱼腥藻和单细胞的集胞藻最近被证明含有一种依赖NAD⁺的双向氢化酶。现在已确定集胞藻基因组的一个5.0 kb DNA片段含有编码双向氢化酶三个亚基的结构基因hoxUYH。集胞藻和多变鱼腥藻中的基因排列明显不同。在集胞藻中，而非多变鱼腥藻中，可以在hoxH下游鉴定出四个辅助基因hoxW、hypA、hypB和hypF。集胞藻hoxH的插入纯合突变体在进行依赖连二亚硫酸钠的氢气释放时完全无活性，但利用氢气的活性几乎是野生型的50%。在任何光合放氧微生物中首个明确的氢化酶突变体的这些发现表明，单细胞蓝细菌集胞藻同时拥有摄取型和双向氢化酶。单细胞非固氮蓝细菌中这两种氢化酶的生理作用尚不清楚。
