The Production of Ammonia by Multiheme Cytochromes c

Abstract

The global biogeochemical nitrogen cycle is essential for life on Earth. Many of the underlying biotic reactions are catalyzed by a multitude of prokaryotic and eukaryotic life forms whereas others are exclusively carried out by microorganisms. The last century has seen the rise of a dramatic imbalance in the global nitrogen cycle due to human behavior that was mainly caused by the invention of the Haber-Bosch process. Its main product, ammonia, is a chemically reactive and biotically favorable form of bound nitrogen. The anthropogenic supply of reduced nitrogen to the biosphere in the form of ammonia, for example during environmental fertilization, livestock farming, and industrial processes, is mandatory in feeding an increasing world population. In this chapter, environmental ammonia pollution is linked to the activity of microbial metalloenzymes involved in respiratory energy metabolism and bioenergetics. Ammonia-producing multiheme cytochromes c are discussed as paradigm enzymes.

Three transcription regulators of the Nss family mediate the adaptive response induced by nitrate, nitric oxide or nitrous oxide in Wolinella succinogenes

“…Taken together, the results suggest that the cells detected the presence of either nitrate, NO or N 2 O and that dedicated signal transduction pathways are likely to exist. It is striking that nitrite and hydroxylamine, both toxic/mutagenic substances, had no effect on the amount of NrfA despite the fact that both compounds are excellent substrates for ammonium production by this enzyme (Einsle et al ., ; Einsle, ; Simon and Kroneck, ; Lockwood et al ., ). Furthermore, it is suggested that the presence of nitrite did not result in NO levels high enough to induce any of the respiratory enzymes.…”

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria

“…succinogenes NrfA has a remarkable substrate range since it catalyses the reduction of nitrite, NO and hydroxylamine to ammonium (Simon & Hederstedt, 2011;Simon & Kroneck, 2014;Stach, Einsle, Schumacher, Kurun, & Kroneck, 2000). NrfA was also reported to produce N 2 O as a product of NO reduction under suitable conditions (Costa et al, 1990) and to react with N 2 O to a so far unidentified product (Stach et al, 2000).…”

“…In contrast to E. coli and other Gammaproteobacteria, the epsilonbacterial NrfA forms a subunit of a membrane-bound menaquinol-reactive complex that also contains a tetrahaem cytochrome c of the NapC-type called NrfH (Einsle, 2011;Kern & Simon, 2008;Rodrigues, Oliveira, Pereira, & Archer, 2006;Simon et al, 2000;Simon & Kroneck, 2014;Fig. 3B).…”

Going with the Electron Flow: Heme Electronic Structure and Electron Transfer in Cytochrome c

“…Heme proteins play many roles in metabolism and in biogeochemical cycles,, processes requiring multielectron redox chemistry. Most biological redox processes make use of series of single ET reactions to carry out multielectron transformations.…”

“…Cyts c play vital roles in a wide range of energy transduction processes ,. Cyts c contain heme c , which is distinguished by its covalent attachment to the polypeptide, usually to two Cys residues in a Cys‐X‐X‐Cys‐His (CXXCH) motif, in which X is any amino acid and His ligates the heme iron (Figure ) ,,,.…”