Authors:Rong-Zhen Liao ^a,b, Jian-Guo Yu ^b, and Fahmi Himo ^a,1
a Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden; and ^b College of Chemistry Beijing Normal University, Beijing, 100875, People’s Republic of China
Proc. Natl. Acda. Sci. U.S.A. 2010, 107, 22523-22527.

Abstract:
Acetylene hydratase is a tungsten-dependent enzyme that catalyzes the nonredox hydration of acetylene to acetaldehyde. Density functional theory calculations are used to elucidate the reaction mechanism of this enzyme with a large model of the active site devised on the basis of the native X-ray crystal structure. Based on the calculations, we propose a new mechanism in which the acetylene substrate first displaces the W-coordinated water molecule, and then undergoes a nucleophilic attack by the water molecule assisted by an ionized Asp13 residue at the active site. This is followed by proton transfer from Asp13 to the newly formed vinyl anion intermediate. In the subsequent isomerization, Asp13 shuttles a proton from the hydroxyl group of the vinyl alcohol to the α-carbon. Asp13 is thus a key player in the mechanism, but also W is directly involved in the reaction by binding and activating acetylene and providing electrostatic stabilization to the transition states and intermediates. Several other mechanisms are also considered but the energetic barriers are found to be very high, ruling out these possibilities.
Link:www.pnas.org/cgi/doi/10.1073/pnas.1014060108

PS:乙炔的水合涉及到CC三键的活化，某些细菌生物体采用钨参与催化过程。目前发现只有三类酶采用钨离子催化反应，也就是乙炔水合酶、醛氧化酶、羧酸氧化酶。自从07年该酶的晶体结构发表后，我就开始寻找可行的反应机理，一直到09年下半年才有突破，期间尝试了至少10多中可能性。最终我们发现不能相信前人关于反应机理基本上所有的假说。简单来说如果有A和B两种情况，前人说A是不可能的，那么你千万不要相信，一定要自己尝试去证明它对还是不对，即使有人证明了，也得仔细看别人做的对不对，里面有哪些近似，这些近似可不可靠。新的发现往往就是你预想不到的，但是如果你真正明白了看起来就非常简单。