Hemoglobin Kinetics of the Galápagos Rift Vent Tube 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 eightfold over the range of 5° to 20°C (k = 2.2 sec^–1at 10°C). Oxygen recombination after flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0° to 20°C(k'_fast = 7 x 10⁶; k'_slow = 1 x 16⁶ liter mole ^–1 sec^–1). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of cooperativity requires that the conformational equilibrium constant L decrease by about 50-fold between 3°and 15°C.