Oxygen equilibria of the hemoglobins from the freshwater catfish Pimelodus maculatus (lacépède, 1803)

Abstract

1. 1. The effect of changes in pH, ATP concentration and temperature upon the oxygen equilibria of the hemoglobin hemolysate from the freshwater catfish Pimelodus maculatus are reported. Chromatography of the hemolysate allowed the isolation of three components, and oxygen equilibrium studies on two of these are also mentioned. 2. 2. Oxygen affinity of the stripped hemoglobin hemolysate from Pimelodus maculatus, at 20 C, in 0.1 M phosphate buffers, varied from a P 50 = 10.6 mm Hg at pH 6.0 to P 50 = 1.8 mm Hg at pH 8.5. The value of n from the Hill equation, an indication of the degree of heme- heme interaction, in the pH range 6.0–8.5, showed minimum values of 1.8 at the extremes of the pH range, and a maximum of about 2.2 at pH 6.8. 3. 3. Oxygen affinity decreases and heme-heme interaction increases, both slightly, in Tris-HCl buffer, pH 7.2, at 20 C, when the molar ratio of ATP to hemoglobin is raised from ~ 0 to 5. 4. 4. The ratio of P 50's at 15 and 25 C is approximately 2.5, with stripped hemoglobin in phosphate buffers. pH 7.O. 5. 5. The hemoglobin hemolysate of Pimelodus maculatus shows three components by ion exchange chromatography. The two with higher relative concentration are homogeneous when analyzed by starch gel electrophoresis. Oxygen equilibrium studies on the two components with higher relative concentration in the hemolysate showed them to behave in a functionally similar way, amongst themselves, and in regard to the whole hemolysate.