Catalytic Mechanism of S-Ribosylhomocysteinase (LuxS): Direct Observation of Ketone Intermediates by 13C NMR Spectroscopy
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- 作者：Jinge Zhu ; Xubo Hu ; Eric Dizin ; and Dehua Pei
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：November 5, 2003
- 年：2003
- 卷：125
- 期：44
- 页码：13379 - 13381
- 全文大小：111K
- 年卷期：v.125,no.44(November 5, 2003)
- ISSN：1520-5126
文摘
S-Ribosylhomocysteinase (LuxS) catalyzes the cleavage of the thioether linkage of S-ribosylhomocysteine (SRH) to produce L-homocysteine and 4,5-dihydroxy-2,3-pentanedione (DHPD). This is a key step in the biosynthetic pathway of the type II autoinducer (AI-2) in both Gram-positive and Gram-negative bacteria. Previous studies demonstrated that LuxS contains a catalytically essential Fe2+ ion. The catalytic mechanism of LuxS was investigated using 2- and 3-13C-labeled SRH as substrate and 13C NMR spectroscopy. These studies revealed the presence of 2- and 3-keto intermediates in the catalytic pathway. The 2-keto intermediate was chemically synthesized, and its chemical and kinetic competence was demonstrated. The results support a catalytic mechanism in which the metal ion catalyzes an internal redox reaction, shifting the carbonyl group from the C-1 position to the C-3 position. Subsequent 
-elimination at the C-4 and C-5 positions releases homocysteine as a free thiol. The results also suggest that Cys-84 and Glu-57 are the possible general acids/bases for proton transfer during catalysis and that the keto intermediates are released from the enzyme active site before rebinding and completion of the reaction.
-elimination at the C-4 and C-5 positions releases homocysteine as a free thiol. The results also suggest that Cys-84 and Glu-57 are the possible general acids/bases for proton transfer during catalysis and that the keto intermediates are released from the enzyme active site before rebinding and completion of the reaction.