Hydrogenase is defined as: "catalyzing the reversible oxidation of molecular hydrogen (H2) and playing a vital role in anaerobic metabolism." The standard catalyzed reaction is H2----> 2H + 2e- Metal containing hydrogenases is divided into three families (Fe hydrogenase, Ni-Fe hydrogenase, and Ni-Fe-Se hydrogenase). If the hydrogenase contains no other metal than Fe they are called the Fe only hydrogenase which contains two families within. The first one is cytoplasmic, soluble, monomeric Fe Hases, and they are found in strict anaerobes such as: Clostriduim pasteruranium and Megasphaera elsdenii. They are extremely sensitive to inactivation by O2 and catalyse both hydrogen evolution and hydrogen uptake. The second group is periplasmic, heterodimeric Fe-Hases from Desulfovibrio which can be purified aerobically and catalyse mainly by H2 oxidation.
These enzymes contain high field ligands such as: cyano and CO (metal carbonyl) which are located in the first coordination sphere of the cluster. Since the cyano and carbonyl ligands are toxic to many biological systems their inclusion in this system play pivotal roles. The high field ligands help ensure that the iron center at the active site remain in a low spin state throughout the catalytic cycle. When the enzyme is isolated in the air a observed oxidized inactive state takes place. However, when the Fe Hydrogenase is fully reduced calculations can show that different oxidation states of the two subunit takes place during the catalytic H2 evolution. Pretty much it should be a Fe(II)-Fe(II) complex with a hydroxyl group (OH) group bonded. Due to the fact that they have high field ligands I would assume that these enzymes would also contain a strong field.
References:
1. Hydrogenase. Wikipedia. 28 February 2011. <http://en.wikipedia.org/wiki/Hydrogenase>.
2. Iron Hydrogenase. 1 February 1999. 28 February 2011. <http://metallo.scripps.edu/PROMISE/FEHASE.html>.
3. Role of Fe hydrogenase in biological hydrogen production. Current Science Vol. 90 No. 12. 25 June 2006. 3 March 2011. <http://www.scribd.com/doc/10453075/Role-of-FeHydrogenase-in-Biological-Hydrogen-Production>.
It was a very interesting blog on Fe-only hydrogenases. Just like Don's MM enzyme, this enzyme has a connection with my environmental chemistry studies. Desulfovibrio bacteria remove toxic substances from the environment by absorbing them and reducing them with these Fe-only hydrogenases. They are involved in what is called bioremediation. I liked that I could connect my other courses to information from your blog :)
ReplyDeleteLots of information to take in in just two paragraphs. Felt to me like you could have written a paper on the topic. But in all seriousness, I felt like some of the things you talked about were not explained, and this could have helped my understanding. An example of this would be when you mentioned Desulfovibrio. If Bilen hadn't mentioned it, I would still be wondering what this is. Desulfovibrio is something completely foreign to me, and it could have maybe enhanced what I got out of the blog. Also, you mentioned the enzyme being in the air, but is it found in any specific organisms other that the Desulfovibrio bacteria? Over all though, good blog.
ReplyDelete-The High School Chemist