© 2001 by The Society for Integrative and Comparative Biology
Nitric Oxide, Invertebrates and Hemoglobin1
1 Duke University, Nicholas School of the Environment Marine Laboratory, 135 Marine Lab Road, Beaufort, North Carolina 28516
Rich redox chemistry of the diatomic NO gives this molecule the functional flexibility to interact with both metal and non-metal components of biological molecules. This important biological signaling and allosteric control has become evident in such varied applications as brain/nervous system function; immune response; growth and development; behavior; and gas transport. Many of the basic discoveries linking NO to biological systems have arisen from structure-function relationships in hemoglobin. For example, by analogy with hemoglobin, Lou Ignarro, in a now-classic paper on NO, proposed that the activation of soluble guanylate cyclase occurs via a NO-driven planar shift in the enzyme's heme iron (Ignarro et al., 1984). Many other proteins involved in NO biology are heme proteins where NO coordination plays an essential function. In this regard, we may view hemoglobin as a microcosm of NO biology.
Invertebrates provide rich examples in which to explore alternate functions, or even perhaps the original functions, of the globins. Oxygen-carrying proteins could well have evolved from metalloproteins that primarily functioned in nitrogen metabolism rather than reversible oxygen binding. Newly discovered aspects of Hb function relate to the signaling and control processes that nitric oxide shows in biological systems. The comparative approach to these processes has played an important role in their elucidation as well as providing rich, intellectual stimulation to those scientists interested in them.