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Moura I, Maia LB, Pauleta SR, Moura JJG. "A bird’s-eye view of denitrification in relation to the nitrogen cycle." In: Moura I, Moura JJG, Pauleta SR, Maia LB, eds. Metalloenzymes in Denitrification: Applications and Environmental Impacts, RSC Metallobiology Series No. 9 (ISBN: 978-1-78262-376-2). Vol. 39. The Royal Society of Chemistry; 2017:. Abstract

This book is devoted to denitrification, an anaerobic process that is used by a wide range of bacteria for energy generation. The overall process involves nitrate, which is present in soil or water, being reduced to gaseous dinitrogen. This initial chapter aims to place denitrification in the larger context of the nitrogen biogeochemical cycle (a bird’s eye view). Detailed topics are developed through the many following contributions. Denitrification is a landscape for probing the structures, functions and mechanisms of action of a wide range of highly specialised metalloenzymes. These carry out, sequentially, four oxo-transfer reactions: NO3 → NO2˙NO → N2O → N2. The environmental implications of these processes are of particular relevance. Nitrate accumulation and the release of nitrous oxide into the atmosphere due to the excessive use of fertilisers in agriculture are examples of two environmental problems in which denitrification plays a central role.

Maia LB, Moura I, Moura JJG. "EPR spectroscopy on mononuclear molybdenum-containing enzymes." In: Hanson G, Berliner LJ, eds. Future Directions in Metalloprotein and Metalloenzyme Research, Biological Magnetic Resonance, Vol. 33 (ISBN: 978-3-319-59100-1). Vol. 12. Cham: Springer Publishers; 2017:. Abstract

The biological relevance of molybdenum was demonstrated in the early 1950s-1960s, by Bray, Beinert, Lowe, Massey, Palmer, Ehrenberg, Pettersson, Vänngård, Hanson and others, with ground-breaking studies performed, precisely, by electron paramagnetic resonance (EPR) spectroscopy. Those earlier studies, aimed to investigate the mammalian xanthine oxidase and avian sulfite oxidase enzymes, demonstrated the surprising biological reduction of molybdenum to the paramagnetic Mo5+. Since then, EPR spectroscopy, alongside with other spectroscopic methods and X-ray crystallography, has contributed to our present detailed knowledge about the active site structures, catalytic mechanisms and structure/activity relationships of the molybdenum-containing enzymes.
This Chapter will provide a perspective on the contribution that EPR spectroscopy has made to some selected systems. After a brief overview on molybdoenzymes, the Chapter will be focused on the EPR studies of mammalian xanthine oxidase, with a brief account on the prokaryotic aldehyde oxidoreductase, nicotinate dehydrogenase and carbon monoxide dehydrogenase, vertebrate sulfite oxidase, and prokaryotic formate dehydrogenases and nitrate reductases.

Maia LB, Moura JJG. "Lessons from denitrification for the human metabolism of signalling nitric oxide." In: Moura I, Moura JJG, Pauleta SR, Maia LB, eds. Metalloenzymes in Denitrification: Applications and Environmental Impacts, RSC Metallobiology Series No. 9 (ISBN: 978-1-78262-376-2). Vol. 41. The Royal Society of Chemistry; 2017:. Abstract

The nitric oxide radical ˙NO (NO) is a signalling molecule involved in several physiological processes in humans, including vasodilation, immune response, neurotransmission, platelet aggregation, apoptosis and gene expression. Undue normal conditions, NO synthases catalyse the formation of NO from l-arginine and dioxygen. Yet, upon a hypoxic event, when the decreased dioxygen concentration compromises NO synthase activity, cells can generate NO from another source: nitrite. Since the late 1990s, it has become clear that nitrite can be reduced back to NO under hypoxic/anoxic conditions. Simultaneously, it was realised that nitrite can exert a significant cytoprotective action in vivo during ischaemia and other pathological conditions. Presently, blood and tissue nitrite are recognised as NO “storage forms” that can be made available in order to maintain NO formation and ensure cell signalling and survival under challenging conditions. To reduce nitrite to NO, human cells can use different metalloproteins that are present in cells for carrying out other functions, including several haemic proteins and molybdoenzymes, forming what we refer to as “non-dedicated nitrite reductases”. In this chapter, two non-dedicated nitrite reductases—xanthine oxidase and myoglobin—will be described, and the human nitrate/nitrite/NO signalling pathway will be discussed within the cellular context and the nitrogen cycle scenario.

Maia LB, Moura I, Moura JJG. "Molybdenum and tungsten-containing enzymes: an overview." In: Hille R, Schulzke C, Kirk M, eds. Molybdenum and Tungsten Enzymes: Biochemistry, RSC Metallobiology Series No. 5 (ISBN: 978-1-78262-089-1). Vol. 28. The Royal Society of Chemistry; 2017:.
Maiti BK, Maia LB, Silveira CM, Todorovic S, Carreira C, Carepo MS, Grazina R, Moura I, Pauleta SR, Moura JJG. "Incorporation of molybdenum in rubredoxin: models for mononuclear molybdenum enzymes." Journal of Biological Inorganic Chemistry. 2015;20:821-829.Website
Moura JJG, Bernhardt PV, Maia LB, Gonzalez PJ. "Molybdenum and tungsten enzymes: from Biology to chemistry and back." Journal of Biological Inorganic Chemistry. 2015;20:181-182.Website
Maia LB, Moura JJG, Moura I. "Molybdenum and tungsten-dependent formate dehydrogenases." Journal of Biological Inorganic Chemistry. 2015;20:287-309.Website
Maia LB, Moura JJG. "Nitrite reduction by molybdoenzymes: a new class of nitric oxide-forming nitrite reductases." Journal of Biological Inorganic Chemistry. 2015;20:403-433.Website
Maia LB, Moura JJG. "How Biology handles nitrite." Chemical Reviews. 2014;114:5273-5357.Website
Moura JJG, Maiti BK, Carreira C, Maia LB, Carepo SP, Pauleta SR, Moura I. "Metal substituted rubredoxins: a sulfur rich coordination site as models for metalloenzymes." Journal of Biological Inorganic Chemistry. 2014;19:731.Website
Maiti BK, Maia LB, Pal K, Pakhira B, Aviles T, Moura I, Pauleta SR, Nunez JL, Rizzi AC, Brondino CD, Sarkar S, Moura JJG. "One electron reduced square planar bis(benzene-1,2-dithiolato) copper dianionic complex and redox switch by O2/HO-." Inorganic Chemistry. 2014;53:12799-12808.Website
Maia LB, Moura JJG. "Nitrite reduction by xanthine oxidase family enzymes: a new class of nitrite reductases." Journal of Biological Inorganic Chemistry. 2011;16:443-460.Website