Summary
The hemolysates isolated from Amazonian stingrays, Potamotrygon sp. are heterogeneous. Their apparent molecular weights, determined by gel filtration, vary from 54,000 - 58,000. Gel filtration experiments of ferro and ferrihemoglobin show that all of the hemolysates are tetramers which do not polymerize upon oxidation. A Bohr effect is evident in oxygen equilibrium experiments of whole blood and of hemolysates. The p1/2 of stripped hemolysates decreases 33-fold between pH 5.95 — 9.0. Neither NaCl nor urea in concentrations up to 4 M significantly affect the oxygen affinity of the stripped hemolysate. The hemoglobin shows cooperative behavior. The n values, determined by the Hill equation, fall within the range 1.0 — 1.6 between pH 6.0 — 9.0, The O2 dissociation and CO combination kinetics were measured by stopped flow spectrophotometry and flash photolysis respectively. The oxygen dissociation rate decreases and carbon monoxide combination rate increases with increasing pH both changing over four-fold between pH 6.3 — 8.8. The oxygen dissociation rate is also phosphate sensitive, increasing approximately 22% in the presence of 1 mM ATP at pH 6.3. Urea denaturation experiments indicate that Potamotrygonid hemoglobin is more stable at high urea concentrations than those of other elasmobranchs and teleosts, being only 50% denatured at urea concentrations greater than 9 M. The oxygen affinity of the blood is higher than those previously reported for many species of marine rays and skates p50 = 12 mm Hg at 30°C in the absence of CO2).