Summary
The hemoglobin of the Amazonian Catfish Pseudodoras sp. was isolated and characterized; it comprises a single component. The hemoglobin's subunit composition is similar to that of other teleost hemoglobins. The apparent native molecular weight as determined by gel filtration is 66,000. The apparent subunit molecular weight is 14,300 by sodium dodecyl sulfate electrophoresis. The hemoglobin does not polymerize after oxidation by potassium ferricyanide. The hemoglobin lacks a Root effect. A small Bohr effects is evident in the phosphate free hemoglobin: Δ log p1/2 /ΔpH is no more than about —0.1 to —0.2 and increases to Δ 1og 1/2 /ΔpH — —0.4 in the presence of 1 mM ΔTP. The cooperativity, as determined by n of the Hill equation, is low, varying from 0.8 to 1.7 between pH 6.1 and 8.6. The p 1/2 values of stripped hemoglobin solutions are extremely low, less than 0.5 mm Hg at all pH values examined between pH 6.1 and 9.0. The high oxygen affinity is reflected primarily in the CO combination rate with resembles that found in myoglobins and isolated subunits of human hemoglobin. Both the CO combination rate and the O2 dissociation rate determined by stopped flow spectrophotometry are pH and phosphate sensitive. Between pH 6.2 and 8.1 the COon rate increases about 5-fold in the phosphate-free hemoglobin. Addition of 1 mM ATP causes a depression in the rate at all pH values examined. The Ooff rate decreases 7-fold going from pH 6.0 to 8.2 is stripped hemoglobin solutions. Addition of 1 mM ATP inducesa ten-fold decrease over the same range. At pH values below 6.0 a depression in the Ooff rate occurs in the stripped hemoglobin, indicative of an acid Bohr effect.