The subunit dissociation properties of turtle hemoglobins

Abstract

1. 1.|The apparent molecular weight of unpolymerized turtle hemoglobins as measured by gel filtration decreases with a decrease in protein concentration. Weights vary from 33 000 to 55 000 within the protein concentration range 0.002–1.2%. 2. 2.|The oxygen affinity of hemoglobin from the turtle, Pseudemys concinna texana, increases slightly when the protein concentration decreases below 0.1% at pH 6.50, but not at pH 8.00. The value of the interaction constant, n, appears to be independent of protein concentration within the range 0.003%–1.0%. 3. 3.|The molecular weight of polymerized hemoglobin appears to depend upon protein concentration only at pH 4.70 where the polymer dissociates upon sufficient dilution. This dissociation probably involves separation of the polypeptide chain subunits of each tetramer but not cleavage of a disulfide linkage. 4. 4.|Polymerization of those turtle hemoglobins capable of aggregation is favored by high pH and conditions promoting methemoglobin formation. At least 80% of the hemoglobin can polymerize to octameric or larger molecules. 5. 5.|Methemoglobin appears to be slightly more dissociated than carboxyhemoglobin under almost all conditions studied.