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Biomedical subjects

O Ristau

Publications and source records attributed to O Ristau.

At least 55 records · Page 3Linked to original sources
PubMed1979

Quantum chemical interpretation of the spectral properties of the CO and O2 complexes of hemoglobin and cytochrome P-450.

The electronic transitions of CO and O2 complexes of hemoglobin and cytochrome P-450 were calculated using a PPP method extended for metal complexes. The calculations show that the unusual spectral properties of cytochrome P-450 are very sensitive to the iron-sulfur bond distance. It is suggested from these calculations that for the conversion of cytochrome P-450 to cytochrome P-420 an increase of the iron-sulfur bond distance of only about 0.2 A is sufficient. The anomalous Soret band of the CO complex as well as the normal Soret band of the O2 complex of cytochrome P-450 are explicable assuming a mercaptide sulfur as fifth ligand.

Animals↗
PubMed1978

Quantitative analysis of the spin equilibrium of cytochrome P-450 LM-2 fraction from rabbit liver microsomes.

The LM-2 fraction of cytochrome P-450 from rabbits in the presence and in the absence of substrate (benzphetamine) is shown to be a thermal mixture of a high spin (S = 5/2) and a low spin (S = 1/2) form each of which exhibiting its individual optical basic spectrum with the Soret maxima at 387 nm and 417 nm for the high spin form and the low spin form, respectively. The equilibrium constants and thermodynamic parameters describing the spin transition and the substrate binding have been evaluated from the temperature and substrate difference spectra, respectively. These two interacting equilibria are presented in terms of a thermodynamic model, which provides a clear quantitative description of the properties of the cytochrome P-450 substrate system. From the thermodynamic model also the cause of the substrate difference spectra can be explained. The importance of the spin shift in the presence of substrate with respect to the reduction rate is discussed.

Animals↗
PubMed1976

Haem accessibility in cytochrome P-450 from rabbit liver. A proton magnetic relaxation study by stereochemical probes.

Cytochrome P-450 was solubilized from phenobarbital induced rabbit liver and purified by affinity chromatography. The longitudinal proton magnetic relaxation rates of this ferric, low-spin sample (as confirmed by ESR) in 20% glycerol aqueous solution are very large compared with low-spin methaemoglobin and myoglobin derivatives. Similarly high rates were measured in a deuterated solution using the aliphatic protons of glycerol as stereochemical markers, which strongly suggests that the haem iron in cytochrome P-450 is much more accessible to the solvent than in harmoglobin or myoglobin. Type I substate (Spasman) produced small but significant increases in NMR rates both in the H2O and in the 2H2O solution, while binding of aniline (Type II substrate) doubled the rates.

Binding Sites↗
PubMed1976

[Quantitative analysis of absorption spectra and spectra of magneto-optical rotatory dispersion of hemoproteins with reference to zero-field splitting. I. Analysis of the divalentcation of deuteroporphyrin in the Q-band region].

I. Analysis of the dication of deuteroporphyrin in the Q-band region. Methods for quantitative analysis of absorption spectra and magneto-optical rotatory dispersion with regard to zero-field splitting of a nearly degenerated term for the latter are described. The methods are based on adaptation of band-form functions to the spectrum using the principle of least squares. Calculation of the zero-field splitting utilizes the formalism evolved by Stephens for strictly degenerated terms (A-terms in the magneto-optical spectrum) which has been further developed to a band-form function depending on zero-field splitting. The curve-form function of the modified A-term contains 4 parameters (zero-field splitting, rotational strength, band width, and the maximum of the band) which have been determined by a computer program. The oscillator and the dipole strength of absorption bands to be calculated simultaneously with the program allows the determination of the magnetic orbital moments of the terms. Exemplified by the dication of deuteroporphyrindimethylester, the significance of zero-field splitting for the recognition of the exact molecule symmetry is demonstrated, and a model of the molecular structure is proposed.

Cations, Divalent↗
PubMed1975

Evidence for the existence of a low spin complex in acidic methemoglobin: its structure and formation.

By means of electron spin resonance and magneto-optical rotation, specific low spin complexes in acidic methemoglobin are obtained. The formation of these complexes is explained by a specific stereochemical arrangement of the distal histidine in the absence of allosteric effectors inducing the formation of a low spin ligand at room temperature. At low temperature, however, the distal histidine is directly bound to the heme iron. As the formation of the low spin complexes depends on allosteric effectors it is suggested that via the distal histidine the affinity of heme iron ligands is modified.

Allosteric Site↗
PubMed1975

[A computer program for the implicit regression of the Hill equation].

A computer program for implicit regression of the Hill equation. The fundamentals for the regression of implicit functions following the Gauss method are dealt with. Basing on these fundamentals a program for the regression of the Hill equation is described. The binding constant, the Hill coefficient and end extinction can be estimated. The mean errors of parameters were calculated in the linear model. The program was written in ALGOL 60 for the computer Robotron 300. The program is available on request.

Computers↗
PubMed1975

[Studies on the magneto-optical rotation of porphyrins, hemins and methemoglobin compounds].

Using the method of magneto-optical rotation (MOR) various porphyrin derivatives, hemin and heme compounds, and a number of methemoglobin complexes were investigated. The spectra were recorded from 450-600 nm; with methemoglobin also in the Soret region. 1. The metalfree porphyrin derivatives (deutero-, meso-, hemato- and protoporphyrins) were measured in strongly acidic aqueous solution. The derivatives thus present as di-cations yield highly resolved MORspectra, where the Q-bands (Oo leads to; Oo leads to 1) originated from the pi-pi transitions of the porphyrin display the curve shape characteristic of an A-term, this proving the presence of the D4h symmetry. An exception is the protoporphyrin, in which the pi-electron system of the porphyrin is perturbed by the influence of pi-electrons of the vinyl group, causing poor resolution, line broadening, and shift of the Q-bands into the lower-energy spectral region. 2. With iron porphyrins (hemin, heme and their complexes) the charge of the iron and the nature of axial ligands determine the position and intensity of the O-bands in the MOR spectrum. Low-spin complexes have a higher symmetry than the high-spin complexes. Whereas with hemin (S = 5/2), the iron located outside the heme plane strongly disturbs the porphyrin pi-system, the high symmetry of porphyrin is greatly retained in the case of heme. This can be explained by the enhanced binding distance between the bivalent iron and the porphyrin to great for a strong coupling between the microsymmetry of the iron and the macrosymmetry of the porphyrin pi-system.

Heme↗
PubMed1975

[Molecular and complex-chemical studies on methemoglobin from Chironomus thummi thummi and various isolated fractions].

1. Six different hemoglobin (Hb) fractions were isolated and characterized from the larvae of Chironomus thummi thummi using column chromatographic procedures. 2. Chromatographic and sedimentation-analytic studies (sedimentation coefficients of 2.0 +/- 0.2 (S)) have shown three Hb fractions to exist basically in a monomeric form. The molecular weight of component M-2 was determined by sedimentation equilibrium technique to be 15,470 +/- 400. The dimeric Hb was found to have sedimentation coefficients of 3.0 +/- 0.1 (S) in the weakly acidic pH region. In alkaline milieu, the reversible dissociation proceeds into the monomeric molecules (S20, W = 1.9 +/- 0.1 (S)). Molecular weights vary between pH 5.7 and 9.8 not only with hydrogen ion concentration, but also with protein concentration in correspondence with a dissociation-association equilibrium consisting of monomers and dimers. 3. For the Hb fraction M-2, a friction ratio of f/fo = 1.03 was calculated, suggesting an almost spherical shape of this protein. In contrast, the dimeric component appears to have a much more asymmetric structure (f/fo = 1.19). 4. The indivdual MetHb fractions bind the ligands: fluoride, imidazole and azide with different affinities.

Diptera↗