Structural and functional studies of hemoglobins isolated from Amazon stingrays of the genus Potamotrygon
1. 1. The hemolysates isolated from Amazonian stingrays, Potamotrygon sp. are heterogeneous. Their apparent molecular weights, determined by gel filtration, vary from 54,000 to 58,000. Gel filtration experiments of ferro- and ferrihemoglobin show that all of the hemolysates are tetrameters which do not polymerize upon oxidation. 2. 2. A Bohr effect is evident in oxygen equilibrium experiments of whole blood and of hemolysates. The p 1 2 of stripped hemolysates decreases 33-fold between pH 5.95 and 9.0. Neither NaCl nor urea in concentrations up to 4 M significantly affect the oxygen affinity of the stripped hemolysate. 3. 3. 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 and 9.0. 4. 4. The O 2 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 and 8.8. The oxygen dissociation rate is also phosphate sensitive, increasing approx 22% in the presence of 1 mM ATP at pH 6.3. 5. 5. 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. 6. 6. The oxygen affinity of the blood is higher than those previously reported for many species of marine rays and skates (p 1 2 = 12 mm HG at 30°C in the absence of CO 2 ). © 1979.
Martin, JP; Bonaventura, J; Fyhn, HJ; Fyhn, UEH; Garlick, RL; Powers, DA
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