Arginine methylation system

NO is a gaseous neurotransmitter implicated in signaling in the central and peripheral nervous system as well as in the immune system and the vasculature. NO is formed from L-arginine by nitric oxide synthase (NOS). There are three isoforms of NOS. All isoforms require NADPH as a cofactor, use L-arginine as a substrate, and are inhibited by Nw-nitro-L-arginine methyl ester (L-NAME). The three isoforms are separate gene products. One isoform of NOS is a cytosolic, calcium/calmodulin-independent, inducible enzyme (iNOS). It is found in macrophages, neutrophils, vascular smooth muscle, and endothelia. The iNOS... 

Demyelination is because of failure of the methylation of arginine of myelin basic protein. The nervous system is especially vulnerable to depletion of S-adenosylmethionine in vitamin B12 deficiency because, unlike other tissues, it contains only methionine synthetase, which is vitamin B12-dependent and not vitamin B12-independent homocysteine methyl transferase that uses betaine as the methyl donor (Section 10.3.4 Weir and Scott, 1995). 

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