Guanidino-nitrogens

As reviewed in Chapter 3 of this book, nitric oxide is the product of the enzymatic oxidation of one of the guanidino nitrogen groups of L-arginine to the free radical nitric oxide and L-citrulline (Marietta etal., 1988). At present there appears to be at least three distinct isoforms of nitric oxide synthase that are primarily differentiated at the level of gene expression (Schmidt, 1992 Nathan,... 

Hibbs, J. B., Jr., Taintor, R. R., Vavrin, Z., Granger, D. L., Drapier, J.-C., Amber, I. J., and Lancaster, J. R., Jr. (1990). Synthesis of nitric oxide from a terminal guanidino nitrogen atom of L-arginine A molecular mechanism regulating cellular proliferation... 

In mammalian cells NO is produced by the oxidation of the terminal guanidino nitrogen of L-arginine (L-arg) by nitric oxide synthase (NOS). According to patent literature, NOS inhibitors have been one of the most intensively investigated research areas in industry of the last couple of years. 

Nitric Oxide (NO) Nitric oxide is a relatively stable free radical synthesized from molecular oxygen and the guanidino nitrogen of arginine (see Fig. 22-31) in a reaction catalyzed by NO synthase. 

Figure 2 Stoichiometry of the enzymatic mechanism of formation of NO, and the structure of a competitive inhibitor, N -monomethyl-L-arginine (NMMA). NO is synthesized by all NOS s by a similar mechanism, involving the NADPH-dependent mixed-function oxidation of a guanidino nitrogen of the amino acid L-arginine (L-arg) to produce L-citrulline (L-cit) and -NO. The nonintegral stoichiometries are explained in the text. NMMA inhibits NOS as a competitive inhibitor...

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