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The ability of Neisseria gonorrhoeae to reduce nitric oxide (NO) may have important immunomodulatory effects on the host during infection. Therefore, a comprehensive understanding of the regulatory mechanism of the nitric oxide reductase gene (norB) needs to be elucidated. To accomplish this, we analysed the functional regions of the norB upstream region. The promoter contains an extended--10 motif (TGNTACAAT) that is required for high-level expression. Deletion and substitution analysis of the norB upstream region revealed that no sequence upstream of the--10 motif is involved in norB regulation under anaerobic conditions or in the presence of NO. However, replacement of a 29 bp inverted repeat sequence immediately downstream of the extended--10 motif gave high levels of aerobic expression of a norB::lacZ fusion. Insertional inactivation of gonococcal nsrR, predicted to bind to this inverted repeat sequence, resulted in the loss of norB repression and eliminated NO induction capacity. Single-copy complementation of nsrR in trans restored regulation of both norB transcription and NorB activity by NO. In Escherichia coil, expression of a gonococcal nsrR gene repressed gonococcal norB; induction of norB occurred in the presence of exogenously added NO. NsrR also regulates aniA and dnrN, as well as its own expression. We also determined that Fur regulates norB by a novel indirect activation method, by preventing the binding of a gonococcal ArsR homologue, a second repressor whose putative binding site overlaps the Fur binding site.

Nitric oxide (NO) is an intercellular signaling molecule; among its many and varied roles are the control of blood flow and blood pressure via activation of the heme enzyme, soluble guanylate cyclase. A growing body of evidence suggests that an additional target for NO is the mitochondrial oxygen-consuming heme/copper enzyme, cytochrome c oxidase. This review describes the molecular mechanism of this interaction and the consequences for its likely physiological role. The oxygen reactive site in cytochrome oxidase contains both heme iron ([a.sub.3]) and copper ([Cu.sub.B]) centers. NO inhibits cytochrome oxidase in both an oxygen-competitive (at heme [a.sub.3]) and oxygen-independent (at [Cu.sub.B]) manner. Before inhibition of oxygen consumption, changes can be observed in enzyme and substrate (cytochrome c) redox state. Physiological consequences can be mediated either by direct 'metabolic' effects on oxygen consumption or via indirect 'signaling' effects via mitochondrial redox state changes and free radical production. The detailed kinetics suggest, but do not prove, that cytochrome oxidase can be a target for NO even under circumstances when guanylate cyclase, its primary high affinity target, is not fully activated. In vivo organ and whole body measures of NO synthase inhibition suggest a possible role for NO inhibition of cytochrome oxidase. However, a detailed mapping of NO and oxygen levels, combined with direct measures of cytochrome oxidase/NO binding, in physiology is still awaited. mitochondria; cytochrome oxidase doi:10.1152/ajpcell.00310.2006