Biochemical predetermination of the NO synthase and nitrite reductase components of the nitric oxide cycle

This review presents some aspects of a concept of cellular evolution bearin g a relationship to nitrate-nitrite respiration, the: endosymbiosis theory, and the origin of NO synthase and nitrite:reductase activity in heme-conta ining proteins. Analysis of structural and functional unity of the NO synth ase and nitrite reductase systems suggests that-these systems-did not arise without any relation. to evolutionarily ancient energetic systems of cells . The use of symmetry principles reveals commonalities among many electron transport chains which in the language of physics is called "invariance"; T his work also comparatively analyzes the nitric oxide cycle and the known n itrogen cycle. The ideas about evolution of the NO synthase and nitrite red uctase systems developed here are clearly compatible with the endosymbiotic theory and the hypothesis that nitrate-nitrite respiration was a precursor of oxygen-dependent respiration.