First 11 pages of thesis. - OPUS - Universität Würzburg

nNOS interacts with several proteins which determine the targeting of
the enzyme or the enzymatic activity. Targeting of nNOS to appropriate sites in
the cell is mediated by its PDZ domain. Some of the proteins that bind to the
PDZ domain and are essential for nNOS targeting are CAPON (carboxy-
terminal PDZ ligand of nNOS), NIDD (nNOS interacting DHHC domain),
dystrophin family of proteins and post-synaptic density proteins (PSD) 93 and
95 100 . Proteins which negatively regulate nNOS activity are protein inhibitor of
nNOS (PIN), nitric oxide synthase-interacting protein (NOSIP) and caveolin-
3 100 . nNOS is also translationally regulated by phosphorylation through
calmodulin-dependent kinases. Phosphorylation of nNOS by calmodulin-
dependent kinase II resulted in a decrease in the enzyme activity whereas
phosphorylation by PKC caused a marked increase in enzyme activity 116 .
Of all the three isoforms of NOS, nNOS was the first enzyme which was
shown to “uncouple”, to produce superoxide instead of nitric oxide 36 . In the
absence of its substrate L-arginine, nNOS catalyses the generation of
superoxide from the oxygenase domain 117 . In the presence of L-arginine nNOS
can generate nitric oxide and superoxide. The ratio of the two radicals depends
on the concentration of the substrate, BH4 117, 118 . Similar to eNOS, BH4 inhibited
superoxide production from nNOS in a dose dependent manner. Interestingly,
L-arginine alone, independent of the dose of BH4 inhibited superoxide
production, suggesting that substrate deficiency but not BH4 deficiency
determines the superoxide production by nNOS 118 . Recently studies have
shown that the methyl arginines, asymmetric dimethyl arginine (ADMA) and N G -
monomethyl L-arginine modulate superoxide as well as nitric oxide generation
from nNOS. Further this study shows that even in the presence of normal
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