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J Peisach

Publications and source records attributed to J Peisach.

At least 145 records · Page 8Linked to original sources
PubMed1977

High resolution EPR studies of the fine structure of heme proteins. Third harmonic detection approach.

When third harmonic detection is applied in EPR studies of the superhyperfine structure of nitrosyl derivatives of a number of human hemoglobin variants, significant resoltuion enhancement is obtained. This has allowed a detailed analysis of the number of superhyperfine lines, their g-values and their splittings, and has led to a more complete understanding of the interaction between the axial ligands of the heme iron. Sudies of the effect of the modulation amplitude on EPR line-shapes revealed that the amplitude required to resolve fine structure in the third harmonic mode is 3-10 times larger than that used to record an undistorted first derivative spectrum. The application of this approach for other systems is discussed, and practical guidelines for its use are given.

Electron Spin Resonance Spectroscopy↗
PubMed1976

Leghemoglobin. An electron paramagnetic resonance and optical spectral study of the free protein and its complexes with nicotinate and acetate.

Electron paramagnetic resonance (EPR) and optical spectra are used as probes of the heme and its ligands in ferric and ferrous leghemoglobin. The proximal ligand to the heme iron atom of ferric soybean leghemoglobin is identified as imidazole by comparison of the EPR of leghemoglobin hydroxide, azide, and cyanide with the corresponding derivatives of human hemoglobin. Optical spectra show that ferric soybean leghemoglobin near room temperature is almost entirely in the high spin state. At 77 K the optical spectrum is that of a low spin compound, while at 1.6 K the EPR is that of a low spin form resembling bis-imidazole heme. Acetate binds to ferric leghemoglobin to form a high spin complex as judged from the optical spectrum. The EPR of this complex is that of high spin ferric heme in a nearly axial environment. The complexes of ferrous leghemoglobin with substituted pyridines exhibit optical absorption maxima near 685 nm, whose absorption maxima and extinctions are strongly dependent on the nature of the substitutents of the pyridine ring; electron withdrawing groups on the pyridine ring shift the absorption maxima to lower energy. A crystal field analysis of the EPR of nicotinate derivatives of ferric leghemoblobin demonstrates that the pyridine nitrogen is also bound to the heme iron in the ferric state. These findings lead us to picture leghemoglobin as a somewhat flexible molecule in which the transition region between the E and F helices may act as a hinge, opening a small amount at higher temperature to a stable configuration in which the protein is high spin and can accommodate exogenous ligand molecules and closing at low temperature to a second stable configuration in which the protein is low spin and in which close approach of the E helix permits the distal histidine to become the principal sixth ligand.

Acetates↗
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↗
PubMed1976

The mechanism of superoxide anion generation by the interaction of phenylhydrazine with hemoglobin.

The mechanism by which superoxide anion is generated by the interaction of phenylhydrazine with either oxy- or methemoglobin was investigated. Rather than superoxide anion generation resulting from an accelerated autooxidation of oxyhemoglobin, it was found that both oxy- and methemoglobin function as peroxidases toward phenylhydrazine with the resultant oxidation of this compound to phenyldiazine. Generation of phenyldiazine from the oxidation of phenylhydrazine by hemoglobin or by the hydrolysis and subsequent decarboxylation of methyl phenylazoformate (C6H5N=NCOOCH3) resulted in the production of superoxide anion. It is suggested that under certain conditions hemoglobin may function as a drug-metabolizing peroxidase.

Azo Compounds↗
PubMed1976

Binding of nitric oxide to reduced L-tryptophan-2,3-dioxygenase as studied by electron paramagnetic resonance.

Ferrous L-tryptophan-2,3-dioxygenase reacts with nitric oxide both in the presence and in the absence of L-tryptophan. Electron paramagnetic resonance studies suggest that the proximal ligand of the heme is a nitrogen atom, probably from an histidyl residue. The interaction of the protein with substrate changes both the symmetry of the paramagnetic center and the mode of interaction of the iron atom with its two axial ligands, NO and the proximal nitrogen atom. Optical absorption and EPR spectra suggest that the affinity of NO for tryptophan dioxygenase increases in the order: tryptophan dioxygenase, tryptophan dioxygenase + alpha-methyltryptophan, tryptophan diogenase " 5-hydroxytryptophan, tryptophan dioxygenase + L-tryptophan. A possible correlation between the number of superhyperfine lines in the EPR spectrum and the affinity of the enzyme for NO is discussed.

Binding Sites↗
PubMed1975

The demonstration of ferrihemochrome intermediates in heinz body formation following the reduction of oxyhemoglobin A by acetylphenylhydrazone.

Interaction of acetylphenylhydrazine with oxyhemoglobin A in a hemolysate or in intact red cells resulted in the formation of ferrihemochromes as shown by a characteristic optical spectrum. The same optical spectrum was observed in a suspension of red cell ghosts containing numerous Heinz bodies. Electron paramagnetic resonance of actylphenylhydrazine-incubated red cells disclosed the presence of previously identified reversible ferrihemochromes, which can be reduced to functional hemoglobin, and irreversible ferrihemochromes, which cannot be reduced to functional hemoglobin. (Ferrihemochromes are defined as low spin forms of ferric hemoglobin having heme ligands endogenous to the protein structure). In contrast, only irreversible ferrihemochromes could be observed in ghosts containing Heinz bodies. In addition both optical and magnetic features of sulfhemoglobin were observed in an acetylphenylhydrazine-treated red cell hemolysate. Similar optical features are produced by the interaction of aromatic nitrogen-containg reductants with purified oxyhemoglobin in the presence of (NH4)2S. This reaction is not effected by the presence of catalase, suggesting that H2O2 is not an intermediate of the reaction. It is concluded that the mechanism of action of acetylphenylhydrazine with oxyhemoglobin is two-fold, ultimate reduction to high spin ferric hemoglobin followed by ferrihemochrome formation. Thus it appears that the pathway of denaturation of hemolytic anemias and thalassemia or induced by chemical reagents, entails a common route involving the formation of ferric hemoglobin by a reductive mechanism, followed by reversible ferrihemochromes, irreversible ferrihemochromes, and ultimately, precipitation.

Chemical Phenomena↗
PubMed1975

Studies on the spin state of 3-methylcholanthrene induced cytochrome P-450 from rat liver.

The time course of infuction of rat liver microsomal cytochrome P-450 by the polycyclic hydrocarbon 3-methylcholanthrene was followed by measuring the specific content of cytochrome P-450, benzpyrene hydroxylase activity, and the percent of cytochrome P-450 existing as the high-spin form (g equal to 7.9, 3.7 and 1.7) as determined by low temperature EPR spectroscopy. Significant increases in benzpyrene hydroxylase, cytochrome P-450 and high-spin ferric hemoprotein are seen twenty-four hours following 3-methylcholanthrene treatment. Administration of DL-ethionine prior to 3-methylcholanthrene treatment effectively blocks any increase in benzypyrene hydroxylase and cytochrome P-450 but not the increase in the levels of the high-spin species of the hemoprotein normally seen following 3-methylcholanthrene induction. In addition, partially purified cytochrome P-450 can be isolated from liver microsomes of 3-methylcholanthrene treated rats as low-spin ferric hemoprotein containing essentially no high-spin species (smaller than 1 per cent). This partially purified hemoprotein has the same substrate specificity as the microsomes from which it was derived. It is therefore concluded that the appearance of the high-spin form of cytochrome P-450, as quantitated by EPR, does not correlate with the induction of cytochrome P-450 and benezpyrene hydroxylase activity by 3-methylcholanthrene.

Animals↗
PubMed1975

An anlysis of the optical titrations of the 430 and 455 NM chromophores of ethyl isocyanide complexes of mammalian hepatic cytochrome P-450.

A computational method is presented from which one may calculate the pK for the spectral changes of the 430 and 455 mm chromophores of ethyl isocyanide complexes of rabbit and rat liver microsomal cytochrome P-450. For the rat liver protein from control or phenobarital-treated animals, the pK for the loss of the 430 nm absorption is approximately equal to the pK for the gain of the 455 nm absorption, confirming that the two chromophores are in pH equilibrium with one another. For a soluble preparation in which the chromophores exhibit the pH equilbrium property, this equilbrium is also maintained even after the addition of ethyl isocyanide. It is concluded that the appearance of a 430 nm absorption after the addition ethyl isocyanide to reduced cytochrome P-450 does not necessarily represent conversion of the protein to cytochrome P-420.

Animals↗