NOSs can be dimeric, calmodulin-dependent or calmodulin-containing cytochrome p450-like hemoprotein that combines reductase and oxygenase catalytic domains in one dimer, bear both flavin adenine dinucleotide ( FAD ) and flavin mononucleotide ( FMN ), and carry out a 5 `-electron oxidation of non-aromatic amino acid arginine with the aid of tetrahydrobiopterin.
32.
Overexpression of several enzymes of the NAD + salvage pathway, including nicotinate phosphoribosyltransferase ( PNC1 ) and nicotinamide mononucleotide adenylyltransferase 1 ( NMNAT1 ) have been shown to extend lifespan in rat models by activating SIRT1 and promoting p53 deacetylation ( van der Veer et al ., 2007; Porcu and Chiarugi, 2005; Arraki et al ., 2004; Berger et al ., 2004; Bedalov and Simon, 2004 ).
33.
Absorbed pyridoxamine is converted to PMP by pyridoxal kinase, which is further converted to PLP by pyridoxamine-phosphate transaminase or pyridoxine 52-phosphate oxidase which also catalyzes the conversion of PNP to PLP . Pyridoxine 52-phosphate oxidase is dependent on flavin mononucleotide ( FMN ) as a cofactor which is produced from riboflavin ( vitamin B 2 ) i . e . in this biochemical pathway, dietary vitamin B 6 cannot be used without vitamin B 2.
