Inducible nitric oxide synthase calcium independent

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... 

Zie QW, Whisnant R, Nathan C. Promoter of the mouse gene encoding calcium-independent nitric oxide synthase confers inducibility by interferon gamma and bacterial lipopolysaccharide. J Exp Med 1993 177 1779-1784. 

NO is an important neuromodulator in the retina, and is implicated in many physiological processes (Goldstein et al., 1996). NO is synthesized from arginine via the action of nitric oxide synthase (NOS). Three distinct isoforms of NOS have been identified. Neuronal NOS (nNOS) and endothelial NOS (eNOS) are Ca -dependent. nNOS is constitutively expressed by certain types of amacrine cells in the retina. These cells often have long projections in the irmerplexiform layer (Sharma et al., 1997 Sharma et al., 2001). eNOS is expressed by the endothelial cells of blood vessels (Cheon et al., 2003). iNOS is Ca -independent and expressed in Muller and RPE cells in response to certain stimuli (Lopez-Costa et al., 1997). Activation of the NMDA receptor leads to an increase in intracellular calcium levels, which can induce expression of, and activate NOS isoforms, either directly (nNOS) or via the activation of calcium-dependent protein kinase C (PKC) (Lipton, 1999) (O Figure 3-6). 

The enzyme nitric oxide synthase (NOS), that produces NO and citrullin from arginine, occurs as several isoenzymes (Knowles et al., 1989). Type I NOS is a constitutive, calcium and calmodulin-dependent enzyme, present in neurons and, possibly, in glia. Type II NOS is calcium-independent and can be induced in macrophages and glial cells by exposure to bacterial lipopolysaccharide (Galea et al., 1992 Murphy et al., 1993). Type III NOS is the endothelial iso-enzyme. NOS-I, II and III are produced by diflferent genes (Bredt et al., 1991 Lamas et al., 1992 Xie et al., 1992 Lowenstein et al., 1992 Lyons et al. 1992 Ogura et al., 1993). NOS displays NADPH-dependent diaphorase... 

It is synthesized from 1-arginine by nitric oxide synthase (NOS) (Moncada et al. 1991). There are two classes of NOS, constitutive NOS (neural type and endothelial type) and inducible NOS (iNOS). Generally, neural NOS and endothelial NOS, whieh are known to generate NO at low concentrations, are expressed constitutively in neurons and endothelial cells, respectively, and their activity depends on elevated intraeytoplasmic calcium/calmodulin levels. On the other hand, iNOS, which generates large amounts of NO for prolonged periods of time, is produced by neutrophils, macrophages, epithelial cells, and many other cell types, and induction of it requires bacterial products or inflammation-associated cytokines independent of calcium/calmodulin concentration (Nathan and Xie 1994 Knowles and Moncada 1994). 

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