Oxygen binding by hemoglobin of the galapagos rift vent worm Riftia pachyptila Jones (Pogonophora; Vestimentifera)

Abstract

Kinetics of the reactions of Riftia pachyptila hemoglobin with oxygen were followed spectrophotometrically by stopped-flow and laser flash photolysis techniques. The rate of oxygen dissociation increases 8-fold over the range 5–20°C ($\text{k = 2.2}\text{s}{}^{\mathrm{-1}}\text{at}\text{10°}\text{C}$). Oxygen recombination following flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0 to 20°C ($\text{k}{}_{\mathrm{<mtext>fast</mtext>}}{}^{\mathrm{\prime }}\text{= 7 · 10}{}^6\text{; k}{}_{\mathrm{<mtext>slow</mtext>}}{}^{\mathrm{\prime }}\text{= 1 · 10}{}^6\text{1 ·}\text{mol}{}^{\mathrm{-1}}\text{·}\text{s}{}^{\mathrm{-1}}$). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of Monod, Wyman and Changeaux (1965, J. Mol. Biol. 12 88–118) requires that the conformational equilibrium constant L decrease by approx. 50-fold between 3 and 15°C.