Comparison study of ferrous ions in deoxygenated Hb-A and its isolated subunits

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.

Cytochrome P450cam and its complexes. Mössbauer parameters of the heme iron

Mössbauer spectroscopy has been used to study the heme iron in various states of cytochrome P450cam from the camphor-hydroxylating system of the bacterium Pseudomonas putida. Native, camphor-free P450cam contains low-spin ferric iron, part of which (approx. 50-70%) is converted to the high-spin ferric state upon addition of camphor. The Mössbauer spectra of the camphor-free enzyme (S equals 1/2) and of the high-spin component (S equals 5/2) of the camphor complex have been successfully simulated using a model based on crystal-field theory and simple convalency considerations. The native low-spin ferric state of P450cam forms a complex with 2-phenylimidazole, with small changes in the g values and Mössbauer spectra. These changes can be accounted for consistently in the crystal-field model referred to above. The addition of putidaredoxin to the camphor-complexed, oxidized P450cam decreases the intensity of the high-spin component and changes its quadrupole splitting. The reduced form of P450cam contrins high-spin ferrous iron, both in the presence and absence of camphor. The complex of reduced P450cam with molecular oxygen is diamagnetic and has a combination of quadrupole splitting and isomer shift that is unusual for a ferrous complex, but strongly resembles that of oxyhemoglobin. These results are compatible with the bound superoxide, Fe3+-O-2, model proposed for oxyhemoglobin (Weiss, J. J. (1964) Nature 202, 83-84). Reduced P450cam and its complexes, oxyP450cam-CO, are all found to be analogous in some respects to the corresponding hemoglobin complexes.

Magnetic susceptibility measurements of deoxygenated hemoglobins and isolated chains

Static magnetic susceptibility measurements have been performed in a wide temperature range (4.5-300 degrees K) on ligquid/frozen solutions of deoxygenated human hemoglobin and its isolated chains. The effects of buffer, pH, dielectric constant and phosphate have been investigated. Measurements have been done also on human fetal chains, on des-Arg and SucNEt-des-Arg hemoglobins. In all the proteins under study of the Fe2+ is the high spin state (S=2). At room temperature the magnetic moments lie in range 4.90 (theoretical spin-only value) to 5.45 Bohr magnetons. Local differences between the iron sites are revealed by the low temperature measurements. A mechanism is proposed to explain the effect of phosphate binding on the magnetic susceptibility.