Functional studies on the single component hemoglobin from an Amazon knife fish,Sternopygus macrurus

Abstract

1. The whole blood of the non-air-breathing gymnotid teleost,Sternopygus macrurus, is half-saturated with oxygen at 5.2 mm Hg (apparent value) at 30°C in the absence of CO2. Addition of 5.6% CO2 causes the apparentP50 value to increase over 3-fold.2. The oxygen affinity of the stripped single-component hemoglobin at 20°C increases about 20-fold between pH 5.8 and 8.6 in the absence of ATP. This difference increases to 100-fold in the presence of 1 mM ATP.3. A substantial Root effect is present: the stripped hemoglobin is only 70% saturated with O2 at pH less than 6 when equilibrated with air.4. The value of the Hill coefficient,n, is maximal near pH 7.0–7.5, and approaches 1.0 at high pH. The value is about 1.5 at low pH in the absence of ATP and 1.0 in the presence of 1 mM ATP.5. The O2 dissociation kinetics are heterogeneous at all pH values but most heterogeneous at low pH. The rate increases substantially as the pH decreases.6. The CO combination kinetics as measured by the stopped flow technique are largely homogeneous except at high pH, but the CO combination kinetics after flash photolysis are markedly heterogeneous.