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W B Mims

Publications and source records attributed to W B Mims.

8 recordsLinked to original sources
PubMed1979

Studies of the electron-nuclear coupling between Fe(III) and 14N in cytochrome P-450 and in a series of low spin heme compounds.

We have observed the nuclear modulation pattern in the envelope of electron spin echoes for various low spin paramagnetic heme proteins including cytochrome c, myoglobin hydroxide, myoglobin mercaptoethanol, and cytochrome P-450, using the three-pulse-stimulated echo method. We have also carried out similar experiments with model compounds containing either [14N]- or [15N]imidazole. In many of the compounds studied, we have been able to identify the nuclear modulation effects arising from 14N of the porphyrin ring and have been able to characterize and interpret the modulation effects due to 14N of various nitrogenous axial ligands. We have found that the heme of low spin ferric cytochrome P-450 is coordinated to a nitrogenous ligand, probably imidazole. We have also demonstrated that the remote 14N of the imidazole ligand in a [14N]imidazole-heme-NO-model compound is coupled differently than in myoglobin nitroxide, demonstrating the direct effect of the protein of metal ligand bonding.

Binding Sites↗
PubMed1979

Measurement of 14N superhyperfine frequencies in stellacyanin by an electron spin echo method.

We have measured the 14N superhyperfine frequencies for weakly coupled nitrogen in stellacyanin and in a model compound Cu(II)-diethylenetriamine-imidazole using a 3-pulse spin echo technique. By making computer simulations of the superhyperfine spectrum, we have been able to show that these frequencies result from the interaction of the remote protonated nitrogen of metal-bound imidazole with Cu(II).

Electron Spin Resonance Spectroscopy↗
PubMed1978

The linear electric field effect in stellacyanin, azurin and in some simple model compounds.

All mononuclear Cu(II) sites in frozen solution are non-centrosymmetric and, unless physically constrained, will have a tetrahedral distortion away from the usual square planar structure often presented for Cu(II) complexes. Blue copper sites such as are found in azurin and stellacyanin have a greater distortion towards a tetrahedral geometry than do simple Cu(II) complexes. The distortion is comparable to that which is observed for Cu(II)-o-phenanthroline dichloride, a known tetrahedral complex. Blue copper sites possess an axis of asymmetry directed away from g parallel which could arise from a metal-sulfur interaction.

Azurin↗
PubMed1977

Pulsed electron paramagnetic resonance studies of types I and II coper of Rhus vernicifera laccase and porcine ceruloplasmin.

Electron spin-echo decay envelopes for types I and II copper of Rhus vernicifera laccase and for type II copper of procine ceruloplasmin have been studied. Nuclear modulation patterns show that imidazole is a ligand for all of them. The linear electric field effect (LEFE) in EPR was studied for type I copper in a laccase preparation from which type II had been removed. The symmetry of the site is near tetrahedral and the magnitude of the LEFE is correlated with the intensity of blue color.

Animals↗
PubMed1977

Linear electric field effect in electron paramagnetic resonance for two bisimidazole--heme complexes, model compounds for B and H hemichromes of hemoglobin and for cytochrome b5.

Bisimidazole-ferric heme is considered to be the structure at the heme site of cytochrome b5 and two different low spin ferric hemochromes spontaneously formed from ferric hemoglobin. The addition of strong base to bisimidazole-ferric heme in organic solvents alters the optical and magnetic properties of this compound. With the use of the linear electric field effect in the electron paramagnetic resonance, we demonstrate that addition of base does not lead to the exchange of hydroxide anion for ligated imidazole and that the bisimidazole structure is retained. Analysis of optical titrations indicates that 2 equiv of base react reversibly with bisimidazole-ferric heme. It is suggested that the two hemichromes formed from hemoglobin differ in structure from one another by the state of protonation of N-1 in the bound imidazoles.

Binding Sites↗
PubMed1976

Assignment of a ligand in stellacyanin by a pulsed electron paramagnetic resonance method.

The electron spin echo decay envelope for the blue copper protein, stellacyanin, and for a number of other Cu(II) complexes has been studied. Particular attention was given to the form of the "nuclear modulation" patterns, which show the effects of coupling between the electron spin and the neighboring nuclei. The envelopes for the hydrated cupric complex and for copper(II) glycylglycine were essentially the same and indicative of the coupling to protons. The peptide complex contains nitrogen nuclei coupled directly to Cu(II), but the coupling constant is so large for these nuclei that a modulation pattern ascribable to 14N is not seen. For copper(II) bovine serum albumin, on the other hand, a contribution due to the coupling of the remote nitrogen belonging to a histidyl imidazole ligand was observed. The modulation pattern for this complex and for stellacyanin closely resembled one another, strongly suggesting that an imidazole is ligated to the copper in this blue protein.

Binding Sites↗