人類活動造成的汞污染無處不在,，而汞對水資源的污染尤為嚴(yán)重。美國研究人員最近找到一種細(xì)菌,，它所合成的酶可降低汞對環(huán)境的污染,。
美國田納西大學(xué)的研究人員發(fā)布公報(bào)說，他們在研究中發(fā)現(xiàn),，汞對靠近食物鏈底端的生物,，如魚及水生貝類的污染相當(dāng)嚴(yán)重，并通過它們最終對人類健康造成影響，但有些細(xì)菌具有破壞這一“污染鏈”的作用,。
研究發(fā)現(xiàn)，一種細(xì)菌所合成的MerB酶可以降低甲基汞的毒性,，從而減小汞對環(huán)境的污染,。這種酶的三維結(jié)構(gòu)能首先擊破甲基汞中汞原子與碳原子的關(guān)鍵鏈接，然后在甲基汞電子四周制造靜電場,，對甲基汞的毒素進(jìn)行分解,。
研究人員將進(jìn)一步探索如何在自然生態(tài)系統(tǒng)中運(yùn)用上述方法減少汞污染。（生物谷bioon.com）
生物谷推薦原始出處：
J. Am. Chem. Soc., 2009, 131 (37), pp 13278–13285 DOI: 10.1021/ja9016123
Mechanism of Hg−C Protonolysis in the Organomercurial Lyase MerB
Jerry M. Parks*†, Hong Guo†‡, Cory Momany§, Liyuan Liang, Susan M. Miller, Anne O. Summers¶ and Jeremy C. Smith†‡
UT/ORNL Center for Molecular Biophysics, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, Georgia 30602-7271, Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th Street, San Francisco, California 94158-2517, and Department of Microbiology, University of Georgia, Athens, Georgia 30602-2605
Demethylation is a key reaction in global mercury cycling. The bacterial organomercurial lyase, MerB, catalyzes the demethylation of a wide range of organomercurials via Hg−C protonolysis. Two strictly conserved cysteine residues in the active site are required for catalysis, but the source of the catalytic proton and the detailed reaction mechanism have not been determined. Here, the two major proposed reaction mechanisms of MerB are investigated and compared using hybrid density functional theory calculations. A model of the active site was constructed from an X-ray crystal structure of the Hg(II)-bound MerB product complex. Stationary point structures and energies characterized for the Hg−C protonolysis of methylmercury rule out the direct protonation mechanism in which a cysteine residue delivers the catalytic proton directly to the organic leaving group. Instead, the calculations support a two-step mechanism in which Cys96 or Cys159 first donates a proton to Asp99, enabling coordination of two thiolates with R−Hg(II). At the rate-limiting transition state, Asp99 protonates the nascent carbanion in a trigonal planar, bis thiol-ligated R−Hg(II) species to cleave the Hg−C bond and release the hydrocarbon product. Reactions with two other substrates, vinylmercury and cis-2-butenyl-2-mercury, were also modeled, and the computed activation barriers for all three organomercurial substrates reproduce the trend in the experimentally observed enzymatic reaction rates. Analysis of atomic charges in the rate-limiting transition state structure using Natural Population Analysis shows that MerB lowers the activation free energy in the Hg−C protonolysis reaction by redistributing electron density into the leaving group and away from the catalytic proton.
