SWEENEY, A.M.; BALSER, E.J.: Neural Hemoglobin in the Polychaete Glycera dibranchiata: Evidence for a Molecular Funnel

Glycera dibranchiata is a common polychaete worm that has a large fluid-filled body cavity, called a coelom, which it uses as a hydrostatic skeleton and as a means of circulating hemoglobin-containing cells (hemocytes) for respiration. The coelomic hemoglobins of G. dibranchiata have been of interest for decades to biochemists and invertebrate physiologists because of their unusual amino acid substitutions and intracellular localization (Volkman et al. 1998, Mangum 1974). We have observed that, in addition to the hemocyte-filled coelomic system, G. dibranchiata also possesses a previously undescribed pumping vascular system. This vascular system lies on the dorsal and ventral surfaces of the gut, and communicates, in the vicinity of the worm�s brain, with a space overlying the ventral nerve cord. This system of blood vessels and circumneural space contain red pigment. The pigment in the nerve cord space has spectral properties of monomeric hemoglobin and an oxygen affinity higher than the monomeric hemoglobin in circulating hemocytes. We hypothesize that this high-affinity respiratory protein in close proximity to the nerve cord acts as a molecular funnel, drawing oxygen from the coelom to respiring nerves.