Reductive bioactivation of nitrates to NO must involve formation of an intermediate species, even if this is a short-lived species at the active site of an enzyme responsible for bioactivation. Before reviewing evidence for the roles of specific enzymes, the potential chemical pathways for this 3e- reduction will be reviewed, with reference to Fig. 5. The overall 3e- reduction may be accomplished by a (2 + 1)e- transfer:
A route via initial single electron transfer has rarely been discussed or elaborated on, although nitrates are good e- acceptors. A radical anion was postulated in the interaction of GTN with sGC, but dismissed by the same workers :
The nitrate radical anion may be an intermediate in flavin-dependent reduction to a nitrite
FlH- + RONO2 + H+ ^ FT" + RONO2" + H+ ^ Flox + RONO + H2O
Model systems are of value in exploring chemical mechanisms of nitrate reductive bioac-tivation and predicting biomolecules able to mediate bioactivation. A catalytically active,
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