Summary
The single hemoglobin component of Brachyplatystoma sp. has been isolated. The CO-hemoglobin has an apparent molecular weight of 69,000 as determined by gel filtration. The hemoglobin displays both acid and alkaline Bohr effects, an organic phosphate effect and no Boot effect. The whole blood p1/2 for oxygen shifts from 10.7 mm Hg in air equilibrated solutions to 25.1 mm Hg after the addition of 5.6% CO2to the equilibration gas. The p1/2 of purified hemoglobin varies from 0.3 mm Hg at pH 8.4 to 4.5 mm Hg at pH 5.9. The Bohr effect measured for stripped hemoglobin between pH 8.0 and 7.0 is Δ log p1/2/ΔpH = -0.23. Additions of 1 mM ATP induce a shift in the Bohr effect to Δ log p 1/2/ΔpH = -0,58 over the same pH range. The n value of stripped hemoglobin solutions varies from l at pH 5.9 to 1.7 at pH 7 0. Additions of 1 mM ATP shift the variation in n to higher pH values, and causes an increase in the n value, n = 2 at pH 7.4. The kinetics of carbon monoxide binding and oxygen dissociation are pH dependent. The COon rate becomes autocatylytic as the pH is lowered, indicating positive subunit interactions. The O2off rate was homogeneous at all pH values. The Bohr effects of Brachyplatystoma hemoglobin and other pimelodid hemoglobins are greater than those determined for the unfractionated hemoglobins of more sedentary species from other catfish families such as the Loricariidae and Callichthyldae.