Structure and Dynamic Behaviour of Heme-Carbon Monoxide of Hemoglobin (HIB) from Lucina Pectinata

Abstract

Three different hemoglobins (HbI, HbII and HbIII) have been isolated from this clam which inhabits in sulfide-rich coastal sediments. Like human, sperm whale and horse myoglobins, Lucina pectinata has a histidine in the proximal position to the heme, however, the distal position E7, is a glutamine residue as in elephant myoglobin. HbI, the monomelic sulfide reactive specie, has, in the Fe+3 oxidation state, an extraordinary affinity for sulfide with fast combination and very slow dissociation dynamics. The other two hemoglobins, HbII and HbIII, resist the reaction with sulfide. The three hemoglobins present unusual dioxygen and carbon monoxide kinetics. These properties may be related to the low distal pocket polarity and the four phenylalanyl residues which do not favor the presence of water molecules in the heme pocket (Kraus et al., 1990). Studies on monomelic hemoglobins, for example HbI, with extreme hydrophobic heme pocket environments can provide useful models for heme proteins to answer: What controls ligand reactivity in these proteins?. How do the heme pocket aromatic residues contribute or modulate the association and dissociation ligand rate constants?.