Tonal nitric oxide and health: anti-bacterial and -viral actions and implications for HIV.

Nitric oxide has been shown to have important physiological regulatory roles, i. e, vasodilation, neurotransmitter release, etc. Now, we review its role as an antibacterial and antiviral agent. Nitric oxide has also been identified as an important factor in the development of non-specific immunity. And accordingly, nitric oxide synthase (NOS), the catalytic enzyme producing nitric oxide, is a key element in the protective activities of nitric oxide. The expression of inducible (i) NOS is regulated by cytokines. iNOS-derived nitric oxide was found to contribute to both early and late phases of antibacterial activity. Enzymes, such as proteases (reverse transciptases, and ribonucleotide reductase, etc.) containing cysteine residues, appear to be targets for nitric oxide nitrosylation, as well as viral-encoded transcription factors that are involved in viral replication. It would appear that this multifunctional signaling molecule is not only involved with signaling between cells, it also appears to maintain the immediate environment free of microbial agents.