Search PubMed⌕ Search

Biomedical subjects

M Brunori

Publications and source records attributed to M Brunori.

At least 325 records · Page 18Linked to original sources
PubMed1978

Properties of cytochrome c modified by attachment to a carbohydrate polymer.

By enzymic digestion of the polysaccharide part of the covalent complex between cytochrome c and Sephadex G-200, a new water-soluble cytochrome c derivative is obtained (called cytochrome cr). Measurement of the free amino groups of this derivative indicates that on average the molar ratio between cytochrome c and polysaccharide is close to 1. Chemical determination of the sugar content gives a value of approx. 24000 for the molecular weight of cytochrome cr. On these bases the soluble cytochrome cr complex may be thought of as a folded protein to which a long polysaccharide tail is covalently bound. The functional behaviour of cytochrome cr is much more similar to that of the native molecule than to that of the insoluble complex (cytochrome ci). In particular the kinetics of the reaction of cytochrome cr and cytochrome cn (native) with ascorbate, ferrocyanide-ferricyanide, O2 and cytochrome c oxidase were investigated in considerable detail. The results of these experiments, together with the observation that the insoluble complex of cytochrome c is a very poor substrate of cytochrome c oxidase [Colosimo, Brunori & Antonini (1976) Biochem. J. 153, (657-661], indicate that hindrance effects constraining the approach between cytochrome cr and its oxidase are of greater importance than specific chemical modifications in determining the functional behavior of the protein.

Cytochrome c Group↗
PubMed1978

Single cell observations of gas reactions and shape changes in normal and sickling erythrocytes.

Microspectrophotometry has been applied to single red blood cells to reinvestigate the linked processes of diffusion of gases inside the erythrocyte and their combination with hemoglobin. The experiments took advantage of the photosensitivity of the cabron monoxide derivative of hemoglobin, which allows ligand release from the CO-saturated red cells under strong illumination and recombination when the light is switched off. The photochemical method was also used to study the kinetics of sickling on ligand removal in single erythrocytes of Hb S carriers. The results give new information on the mechanism of the sickling process.

Anemia, Sickle Cell↗
PubMed1978

A macromolecular transducer as illustrated by trout hemoglobin IV.

Oxygen binding by trout Hb IV has been investigated as a function of pH up to 10 atmospheres (1 MPa) of pure O2. The results bring out an extreme proton-oxygen linkage, which gives rise to a Root effect. They are discussed in relation to the function of the hemoglobin as an oxygen pump. The system is of special interest as providing a prototype of a macromolecule acting as a transducer by coupling two allosterically linked reactions.

Allosteric Regulation↗
PubMed1977

Determination of red blood cell superoxide dismutase and glutathione peroxidase in newborns in relation to neonatal hemolysis.

Superoxide dismutase and glutathione peroxidase activities have been determined in newborns. Their mean values are approximately the same as in normal adults. In some cases a low content of superoxide dismutase and/or a high (superoxide dismutase/glutathione peroxidase) ratio are associated with hematological symptoms. In addition, a low superoxide dismutase activity is associated with hyperbilirubinemia and is present in two of the three cases showing maximal acetylphenylhdrazine-induced hemoloysis.

Adult↗
PubMed1977

Reactivity of ferrous myoglobin at low pH.

The rates of reaction of myoglobin with carbon monoxide at low pH are reported. The pH versus rate profile of these kinetics resembles that found for heme model compounds, revealing an increase in combination rate at low pH. These facts suggest that CO binding by myoglobin changes from a mechanism of "direct ligant association" at pH 5 to a mechanism, similar to that proposed for heme model compounds, which assumes a tetracoordinated intermediate as a result of the protonation of the proximal imidazole.

Animals↗
PubMed1977

The electron-transfer reaction between azurin and the cytochrome c oxidase from Pseudomonas aeruginosa.

A stopped-flow investigation of the electron-transfer reaction between oxidized azurin and reduced Pseudomonas aeruginosa cytochrome c-551 oxidase and between reduced azurin and oxidized Ps. aeruginosa cytochrome c-551 oxidase was performed. Electrons leave and enter the oxidase molecule via its haem c component, with the oxidation and reduction of the haem d1 occurring by internal electron transfer. The reaction mechanism in both directions is complex. In the direction of oxidase oxidation, two phases assigned on the basis of difference spectra to haem c proceed with rate constants of 3.2 X 10(5)M-1-S-1 and 2.0 X 10(4)M-1-S-1, whereas the haem d1 oxidation occurs at 0.35 +/- 0.1S-1. Addition of CO to the reduced enzyme profoundly modifies the rate of haem c oxidation, with the faster process tending towards a rate limit of 200S-1. Reduction of the oxidase was similarly complex, with a fast haem c phase tending to a rate limit of 120S-1, and a slower phase with a second-order rate of 1.5 X 10(4)M-1-S-1; the internal transfer rate in this direction was o.25 +/- 0.1S-1. These results have been applied to a kinetic model originally developed from temperature-jump studies.

Azurin↗
PubMed1977

Properties of trout hemoglobin covalently bound to a solid matrix.

This paper reports the ligand binding properties of the major hemoglobin component from trout (Salmo irideus) covalently bound to a solid matrix (Sepharose or Sephadex). A comparison between the functional properties of this protein in solution and of the protein-matrix complex shows significant changes although the basic properties of the molecule are maintained on covalent binding to Sepharose (or Sephadex). Thus the Root effect, characteristic of Hb trout IV, is still present while the heme-heme interactions are, on the average, smaller in the matrix bound protein as compared to the soluble form. No differences in the O2 binding properties were observed when the protein was coupled to the resin, as the ligand bound or as the ligand free derivative. Although an unequivocal interpretation of the data is made difficult by the lack of information on the number and identity of the groups involved in the coupling, the main changes in the protein functional properties may be related to the chemical modifications "per se" more than to the immobilization imposed to the macromolecule by coupling to the matrix. Structural changes which mainly involve perturbation of the tertiary structure of the molecule may qualitatively rationalize the data.

Animals↗
PubMed1977

Chromous ion reduction of mammalian cytochrome oxidase and some of its derivatives.

The reduction of cytochrome c oxidase by Cr2+, followed by means of stopped-flow spectrophotometry, exhibits two phases: the faster Cr2+-concentration-dependent reaction has an initial rate constant of 1.1 X 10(4)M-1-S-1, but reaches a rate limit at high concentration of reductant; the slower phase is concentration-independent with a rate of 0.3S-1. The activation energies of the fast and the slow processes are 35 and 71 kJ/mol respectively. The reduction kinetics of the mixed-valence CO complex and the cyanide-inhibited enzyme were compared with those of the fully oxidized forms: both the liganded species have a fast phase identical with that found in the oxidized oxidase. A comparison of the kinetic difference spectra obtained for the fast phase of reduction of oxidized oxidase with those obtained on reduction of the liganded species suggests that the rapid phase arises from the reduction ofhaem a, and the slow phase from the reduction of haem a3.

Chromium↗
PubMed1977

A kinetic study of the pH-dependent properties of the ferric undecapeptide of cytochrome c (microperoxidase).

The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperature-jump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the feric iron while the second and third arise from the binding of the two available amino groups present (the alpha-NH2 of valine and the epsilon-NH2 of lysine). Molecular models indicate that steric retraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide. Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 X 10(6) M-1 s-1 for the intrinsic combination constant of CN- anion with the haem. A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.

Animals↗
PubMed1977

The effect of macromolecular polyanions on the functional properties of human hemoglobin.

The binding of dextran sulphate and heparin to human hemoglobin and their effect on the properties of gas transport have been investigated. Both dextran sulphate and heparin are strongly bound by oxy-hemoglobin as well as deoxyhemoglobin and the stoichiometry of the binding (polyanion/tetrameric hemoglobin) is less than unity; sedimentation analysis gives indication for the existence of octomers. The oxygen affinity of hemoglobin is decreased, to the same extent, by both dextran sulphate and heparin. This effect is pH-dependent. In addition the polyanions affect the position and the magnitude of the Bohr effect. In the presence of dextran sulphate the recombination of hemoglobin with carbon monoxide after flash photolysis is biphasic and the fraction of quickly reacting material increases with dilution of the protein.

Dextrans↗
PubMed1977

Functional properties of partially oxidized trout hemoglobins.

This paper reports on a study of the effect of partial oxidation on oxygen and carbon monoxide binding by components I and IV of trout hemoglobin. The O2 binding equilibria of the various oxidation mixtures show a decrease in the heme-heme interactions as the number of oxidized sites is increased. However, the large Bohr effect, characteristic of Hb Trout IV, is maintained unchanged. Similarly the time course of CO combination changes on increasing the fractional oxidation, and the autocatalytic character of the CO binding kinetics is lost; however the pH dependence of the apparent "on" constant in the oxidation mixtures is similar to that characteristic of the native molecule. The results of the O2 equilibria and of CO binding kinetics may be interpreted in accordance with the two state concerted model suggesting that in the oxidation intermediates there is an increase in the fraction of the high affinity (R) conformation. Additional experiments on the effect of azide, and fluoride, ferric ligands which produce a change of spin state of the heme iron, suggest that additional second order conformational changes may also come into play.

Animals↗