Circular dichroism as a probe of the allosteric R in equilibrium T transformation in hemoglobins and modified hemoglobins.

The circular dichroism spectra at pH 6.5 of a number of hemoglobins and modified hemoglobins have been recorded in the 280 nm region and interpreted in terms of shifts of the R?T allosteric transformation. Inositol hexaphosphate converts aquomet hemoglobin A(S) to the T form but the carbamlyated derivatives are unaffected by inositol hexaphosphate and remain in the R form. Fluorodinitrobenzene and dimethyl adipimidate modified hemoglobins are locked in an intermediate form, and inositol hexaphosphate has little or no effect. The circular dichroism in the 280 nm region is shown to be a useful diagnostic tool for chemical agents that affect the R?T allosteric transformation.