![]() ![]() ![]() Then, they describe the incisive mechanistic studies that have led to our understanding of how heme oxygenase catalyzes the amazing degradation of heme to biliverdin, CO and Fe(II) in a reaction that requires seven electrons and three oxygenation cycles. Rivera and Rodriguez begin by pointing out the Janus nature of CO both as a toxin (at high levels) and as a cytoprotective molecule. The NiFe hydrogenase review by Fontecilla-Camps also covers the surprising biosynthesis of the intrinsic CN ligand from carbamoyl phosphate future studies will be required to elucidate the origin of CO in these proteins.ĬO again takes center stage in chapter 8, which describes the synthesis of CO during heme breakdown catalyzed by heme oxygenase. Another common striking feature of these three classes of enzymes is that they undergo competitive inhibition by CO and CN. ![]() Remarkably, these three classes of convergently evolved enzymes form Fe-CO (and Fe-CN in the and enzymes) bonds to stabilize a low-spin low-valent iron center, thus, promoting the catalytic cleavage and formation of hydrogen gas. The next three chapters on the, , and hydrogenases, respectively, continue the theme of metal complexes with diatomic metals. However, of these, the paramagnetic Ni-CO complex on acetyl-CoA synthase is the only species that has been trapped and demonstrated to be a catalytically competent intermediate. Chapter 4 by Lindahl describes the remarkable mechanisms of acetyl-CoA synthase, which appears to generate acetyl-CoA through a series of organometallic methyl-Ni, Ni-CO, and acetyl-Ni intermediates, and of carbon monoxide dehydrogenase, which forms a Ni-CO intermediate during CO oxidation. This chapter includes the evidence for and against the intermediacy of methylnickel in catalysis by this enzyme. Chapter 3 by Jaun and Thauer covers the model chemistry and enzymology related to the formation of a methylnickel intermediate in methyl-coenzyme M reductase and the subsequent generation of methane from this organometallic intermediate. The next two chapters cover the other major enzymatic systems that appear to generate organometallic intermediates during their catalytic mechanisms: the nickel-dependent methylcoenzyme M reductase and acetyl-CoA synthase/carbon monoxide dehydrogenase. Chapter 2 by Matthews, which authoritatively covers the biochemistry of enzymes that utilize or form methyl- or adenosylcobalamin, features exciting recent structural and mechanistic insights into the properties of these two important classes of bioorganometallic systems and how they promote nucleophilic versus radical cleavage/formation of the carbon-cobalt bond. This chapter will serve as a valuable resource for scientists to relate the properties of B 12 enzymes to those of model systems. The first one, by Kräutler, focuses on the chemical structure and reactivity of methyl- and adenosylcobalamin and on the thermodynamics and kinetics of the redox chemistry that control formation and lysis of the carbon-cobalt bond. The book is recommended for researchers studying any subject relating to transition metal and organometallic chemistry and to the roles of metals in biology.Ĭoenzyme B 12 was the first metal-carbon bond described in an enzyme thus, it is fitting that the volume open with two chapters on vitamin B 12 chemistry and biochemistry. It also describes systems in which the metal-carbon bond represents an inhibited state of an enzyme and ways that chemists use the organometallic bond to probe the active site of an enzyme. The volume describes ways that nature uses the organometallic bond to house a latent radical, to stabilize the catalytically active electronic state of a metal ion, and to activate a substrate in an enzymatic reaction. The book includes 12 chapters, all authored by experts in their particular area. ![]() The sixth volume in the Metal Ions in Life Sciences series, “Metal-Carbon Bonds in Enzymes and Cofactors”, is a comprehensive and authoritative reference covering the current understanding of naturally occurring metal-carbon bonds. ![]()
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