The isolation and characterization of the hemoglobin ofBrachyplatystoma sp.: A tropical catfish

Abstract 1. 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. 2. The hemoglobin displays both acid and alkaline Bohr effects, as organic phosphate effect and no Root effect. The whole blood p 1/2 for oxygen shifts from 10.7 mm Hg in air equilibrated solutions to 25.1 mm Hg after the addition of 5.6% CO 2 to the equilibration gas. The p 1/2 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 isΔlog p 1/2 /ΔpH= −0.23. Additions of 1 mM ATP induce a shift in the Bohr effect toΔlog p 1/2 /ΔpH= −0.58 over the same pH range. 3. The n value of stripped hemoglobin solutions varies from 1 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 cause an increase in the n value ( n = 2 at pH 7.4). 4. The kinetics of carbon monoxide binding and oxygen dissociation are pH dependent. The CO on rate becomes autocatalytic as the pH is lowered, indicating positive subunit interactions. The O 2 off rate was homogeneous at all pH values. 5. 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 Callichthyidae.