Paramagnetic proton nuclear magnetic resonance shifts of metmyoglobin, methemoglobin, and hemin derivatives

Heme methyl hyperfine-shifted nuclear magnetic resonance peaks assigned by selective deuteration as indicators of heme-protein interactions in metmyoglobins

The heme methyl resonances in a variety of high-spin, low-spin and spin-equilibrium forms of sperm whale metmyoglobin have been assigned by reconstituting myoglobin with selectively deuterated hemes. Two patterns for the heme methyl hyperfine shifts are observed, one characteristic of the low-spin state and the other typical of the high-spin state. The two protein forms which can change the position of their spin equilibrium significantly with changing temperature exhibit the pattern of the dominant spin state component at any temperature. The different hyperfine shift patterns for the low-spin and high-spin states are concluded to arise not from different heme-protein contacts in the two spin states, but from characteristic differential sensitivities of the dominant spin transfer mechanisms to the same rhombic perturbation.

Nuclear magnetic resonance study of heme-heme interaction in hemoglobin M Milwaukee: implications concerning the mechanism of cooperative ligand binding in normal hemoglobin

Hemoglobin M Milwaukee (beta 67E11 val leads to Glu) is a naturally occurring valency hybrid containing two permanently oxidized hemes in the beta-chains. In this mutant, the two abnormal beta-chains cannot combine with oxygen, whereas the two alpha-chains are normal and can combine with oxygen cooperatively with a Hill coefficient of approximately 1.3. High-resolution proton nuclear magnetic resonance spectroscopy at 250 MHz has been used to investigate the hyperfine shifted resonances of the abnormal ferric beta-chains of Hb M Milwaukee over the spectral region from -30 to -60 parts per million from water at pD 7 and 30 degrees.

Proton magnetic resonance studies of peroxidases from turnip and horseradish

Proton NMR spectra at 270 MHz have been measured for horseradish peroxidase and turnip peroxidase isoenzymes (P1, P2, P3 and P7) in both their high spin ferric native states and as the low spin ferric cyanide complexes. Resonances of amino acids near the heme have been identified and used to investigate variations in the structure of the heme crevice amongst the enzymes. Ligand proton resonances have been resolved in spectra of the cyanide complexes of the peroxidases and these provide information on the heme electronic structure. The electronic structure of the heme and the tertiary structure of the heme crevice are essentially the same in the acidic turnip isoenzymes, P1, P2 and, to a lesser extent, P3 but differ in the basic turnip enzyme, P7. The heme electronic structure and nature of the iron ligands in peroxidases are discussed. Further evidence is presented for histidine as the proximal ligand. A heme-linked ionizable group with a pK of 6.5 has been detected by NMR in the cyanide complex of horseradish peroxidase.

NMR studies of hemoproteins. VI. Acid-base transitions of ferric myoglobin and its imidazole complex

220 MHz proton NMR was applied to the acid-base transition of ferric myoglobin and its imidazole complex. In horse and sperm whale ferric myoglobins: (1) pH-dependent shift of heme-ring methyl signals above p2H 10 was analyzed on the basis of rapid exchange between alkaline and acidic forms by the use of pK value 9.1 of acid-base transition in 1H20 solution; (2) limiting shifts of three methyl signals were reasonably determined for purely alkaline form. For the imidazole complex: (3) a drastic high field shift of each signal was observed above p2H 9.0, whereas N0methyl imidazole complex did not exhibit such a shift, which suggests the 2H+ dissociation from liganded imidazole greater than N2H. It is concluded thns.

Magnetic and spectroscopic probes for FeOFe linkages in hemin systems

Magnetic and spectroscopic properties of mu-oxo-bis-hemins from natural and structurally related porphyrins were investigated as probes for ascertaining the presence or absence of FeIII-O-FeIII linkages between hemin moieties of hemeproteins. Magnetic susceptibilities of solids from 2.2 to 293 degrees K were investigated. The data fit the temperature variations expected for a pair of antiferromagnetically coupled S = 5/2, iron (III) porphyrins with J values of 175, 190, 195, 205, and 210 degrees K for deuterohemins with hydrogen, vinyl, 2'-ethoxycarbonylcyclopropyl, acetyl, propionyl, and ethyl 2,4-substituents, respectively. This magnetic character is reflected in PMR spectra that exhibit resonances with far less broadening and paramagnetic shift than is the case for monomeric high-spin hemins. Only impurities are seen in EPR spectra, which serve effectively in monitoring the magnetic purity of preparations. An infrared active asymmetric stretching frequency characteristic of the FeOFe linkage can be identified by substitution of 160 by 180. Electronic spectra are highly characteristic with poorly resolved absorption bands. The substituents on the porphyrin ring exert significant, but usually not large, electronic and steric effects on these properties. Solvent effects were relatively small and no firm evidence for binding of ligands trans to bridging oxygen was found. The uniqueness of these physical properties and their low sensitivity to changes in porphyrin structure or medium facilitates the identification of mu-oxo linkage in hemins or oxidized hemeproteins.

Proton magnetic resonance studies of the ferredoxins from spinach and parsley

Contact-shifted resonances have been detected in the pmr spectra of both oxidized and reduced forms of spinach and parsley ferredoxins. These resonances are assigned to the beta-CH(2) protons of four cysteine residues that are thought to bind the iron-sulfur redox center to the polypeptide chain. Temperature dependences of contact shifts reveal that the two iron atoms are antiferromagnetically coupled in both redox forms of each of these proteins. Thermal population of magnetic states gives rise to the contact shifts observed in the formally diamagnetic oxidized forms of these ferredoxins and accounts for the failure of contact shifts in the reduced forms exhibit to a Curie Law temperature dependence. It appears that the unpaired electron of reduced spinach and parsley ferredoxin is unequally distributed over the two iron centers. Valence states for the iron pairs of high-spin Fe(+3)-Fe(+3) and Fe(+2)-Fe(+3) for the oxidized and reduced forms, respectively, are compatible with the nmr results.

Proton magnetic resonance study of ferredoxin from Clostridium pasteurianum

Magnetic susceptibilities of both reduced and oxidized ferredoxin from Clostridium pasteurianum were obtained in solution. Whereas the reduced form exhibits a Curie law behavior, the magnetic susceptibility of oxidized ferredoxin in fact increases with temperature and suggests extensive antiferromagnetic exchange coupling between the component iron atoms. Contact-shifted resonances are observed for both forms of ferredoxin that are attributed to the beta-CH(2) protons of the eight cysteine residues. A model based on these results is presented.

Nuclear magnetic resonance studies of hemoglobins. 3. Evidence for the nonequivalence of alpha- and beta-hains in azide derivativeof methemoglobins

Nuclear magnetic resonance spectroscopy (100-MHz proton) was used to study the low-spin (S = 1/2) azide derivatives of human adult (alpha(2)beta(2)), human fetal (alpha(2)gamma(2)), Zürich (alpha(2)beta(2) (63 His --> Arg)), and horse (alpha(2)'beta(2)') methemoglobins, as well as whale metmyoglobin in 0.1 M deuterated phosphate at pD 7 and at 31 degrees C. The experimental results indicate that the azide-bound heme groups of the alpha- and beta-chains in human adult methemoglobin and of the alpha- and gamma-chains in fetal methemoglobin are not equivalent. The affinity of the beta- or gamma-chain for azide ion appears larger than that of the alpha-chain. The nuclar magnetic resonance spectrum of hemoglobin Zürich shows that the environment of the azide-heme complex in the abnormal beta-chain is altered by the substitution of arginine for histidine in the beta-63 position, while the alpha-heme environment remains unaffected.

Proton magnetic resonance studies of porphyrin iron (3) cyanides

The nuclear magnetic resonance (NMR) spectra at 220 Mc of cyanodeuteroporphyrin IX dimethyl ester iron (III), cyanoprotoporphyrin IX diethyl ester iron (III), and cyanoprotoporphyrin IX iron (III) in a mixed solvent of 80 per cent d(5)-pyridine and 20 per cent D(2)O have been measured. The resonances are assigned and, except for the ester alkoxy groups, are shown to be shifted by temperature-dependent hyperfine interactions with Fe (III). From the experiments, upper limits are placed upon the pseudocontact contributions, and values of the contact interactions are derived. Spin densities in carbon pi-orbitals are calculated from the contact shifts and discussed in terms of preliminary Hückel calculations.