ChemInform Abstract: Nitric Oxide in Biological Denitrification: Fe/Cu Metalloenzyme and Metal Complex NO_x Redox Chemistry

Abstract

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Roles of glutamates and metal ions in a rationally designed nitric oxide reductase based on myoglobin

“…While being able to design such functional proteins is laudable, the impact of such an achievement would be greater if the designed proteins can be used to address fundamental issues in chemistry and biology that are difficult to tackle by other methods. One primary example is the roles of conserved glutamates and metal ions in bacterial nitric oxide reductase (NOR) (17)(18)(19).NO is critical for all life (20). Bacterial denitrification is a crucial part of the nitrogen cycle in nature that involves a four-step, five-electron reduction of nitrate (NO 3 − ) to dinitrogen (N 2 ) (17, 19).…”

“…Despite these successes, the roles of the conserved glutamates and metal ions still remain to be fully elucidated, partly because of the difficulty in obtaining native NOR in high yield and the lack of a 3D structure. Even if these problems are resolved, it is still difficult to replace iron in the native Fe B site with other metal ions, and spectroscopic studies of native NOR are often complicated by the presence of other metal cofactors (e.g., low-spin heme).To overcome these limitations, a number of synthetic models of NOR using small organic molecules as ligands, have been made in which the nonheme Fe B site can be replaced by a copper ion (17,(38)(39)(40)(41)(42)(43)(44)(45). In addition, since these model systems lack additional metal-binding sites, spectroscopic studies are often simplified.…”

“…Bacterial denitrification is a crucial part of the nitrogen cycle in nature that involves a four-step, five-electron reduction of nitrate (NO 3 − ) to dinitrogen (N 2 ) (17,19). Bacterial NOR is a membrane-bound protein that catalyzes one step of this process, namely, the two-electron reduction of NO to N 2 O (17,19).…”

“…Bacterial denitrification is a crucial part of the nitrogen cycle in nature that involves a four-step, five-electron reduction of nitrate (NO 3 − ) to dinitrogen (N 2 ) (17,19). Bacterial NOR is a membrane-bound protein that catalyzes one step of this process, namely, the two-electron reduction of NO to N 2 O (17,19). With no crystal or solution structure available for bacterial NOR to date, sequence alignments and homology modeling (21,22) have indicated that NOR is structurally homologous to the largest subunit (subunit I) of hemecopper oxidases (HCOs) (23), enzymes that catalyze reduction of O 2 to water.…”

“…To overcome these limitations, a number of synthetic models of NOR using small organic molecules as ligands, have been made in which the nonheme Fe B site can be replaced by a copper ion (17,(38)(39)(40)(41)(42)(43)(44)(45). In addition, since these model systems lack additional metal-binding sites, spectroscopic studies are often simplified.…”