Dependence of magneto-optical rotatory dispersion and magnetic circular dichroism of deoxy- and methemoglobin on their quaternary structure.

Methods of magnetic optical activity, magneto-optical rotatory dispersion (MORD) and magnetic circular dichroism (MCD), were shown to be sensitivie to the quaternary structure of deoxyhemoglobin. The isolated alpha and beta chains, the monomeric hemoglobins (leghemoglobin, fraction III of Chironomus thummi thummi hemoglobin) and hemoglobin in the R state (hemoglobin digested with carboxypeptidases A and B) exhibit in the visible region two MORD minima of equal intensities. In native tetrameric hemoglobins studied (human, horse, porcine, feline, carp, tortoise, frog) the ratio of the intensities of these MORD minima is about 2. The MORD data for deoxy-des Arg-N-ethylsuccinimide-hemoglobin indicate that in solution there is a mixture of the T and R states, the equilibrium between the states being shifted toward the R structure. The identity of the MORD curves for deoxy-bis(N-maleimidoethyl)-ester-hemoglobin and for native deoxyhemoglobin indicates that deoxy-bis(N-maleimidoethyl)ester-hemoglobin has the T structure in solution. Comparison of the MORD curves exhibited by a native methemoglobin, a native metmyoglobin and the modified hemoglobins in the met form in the absence and presence of organic and inorganic phosphates reveals no direct correlation between the MORD changes and methemoglobin quaternary structure.