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Biomedical subjects

J Léonis

Publications and source records attributed to J Léonis.

At least 37 records · Page 2Linked to original sources
PubMed1977

The alteration of the functional properties of human haemoglobin by spectrin.

Kinetic investigation by means of stopped flow techniques showed the rate of deoxygenation of haemoglobin to be slower in the presence of spectrin. At pH 7.15, the kinetic constant was 27.2 sec-1 in presence of spectrin instead of 34.3 sec-1 for haemoglobin alone. Also, equilibrium studies have revealed that the oxygen pressure for half-saturated haemoglobin decreased when spectrin was added to the reaction medium. At pH 7.35, the log (pO2)1/2 was 0.88 for haemoglobin in presence of spectrin instead of 0.93 for haemoglobin alone. From these results, an interaction between spectrin and haemoglobin may be suspected.

Hemoglobins↗
PubMed1976

Study of the biological significance of cytochrome methylation. I. Thermal, acid and guanidinium hydrochloride denaturations of baker's yeast ferricytochromes c.

The iso-cytochromes c from baker's yeast: iso-1 methylated and unmethylated forms and iso-2 have been purified and their stabilities towards denaturants compared to that of horse heart cytochrome c. Thermal, acid and guanidinium hydrochloride denaturations were followed using fluorescence emission of their tryptophan 59 and/or the absorbance in the Soret region as the physical parameters. Very few differences could be evidenced among the ferricytochromes investigated in this study insofar as the acid denaturations are concerned. This is to be contrasted with the conclusions of the thermal and guanidinium hydrochloride denaturations studies which clearly showed the ferricytochrome from horse heart to be much more stable than those from baker's yeast. No appreciable differences could be measured among the methylated and unmethylated forms of iso-1 cytochrome c nor among iso-1 and iso-2 cytochromes from baker's yeast. Our results suggest that a stabilizing effect of methylation on the tridimensional structure of ferricytochrome c must probably be discarded. Other possible physiological roles of methylation are suggested taking into account the relative instability of ascomycetes's cytochromes as compared to mammalian ones.

Animals↗
PubMed1976

Iso-cytochrome c species from baker's yeast. Analysis of their circular-dichroism spectra.

The circular-dichroism spectra of baker's-yeast iso-1- (methylated and unmethylated forms) and iso-2-cytochrome c species were examined between 200 and 600nm. In the visible region the yeast haemoproteins have characteristics nearly indistinguishable from those of horse heart cytochrome c. From the spectra in the u.v. region the latter appears, however, to be more helical. It is proposed that the likely element of non-helical structure in iso-1-cytochrome c is residues 62-70.

Animals↗
PubMed1976

A comparative study of the thermal denaturation parameters of lysozyme in the dissolved and crystalline states.

Differential scanning calorimetry was used for investigating the conformational changes of lysozyme resulting from the combined actions of temperature and of denaturants at various concentrations. The transition temperatures, for the protein in the dissolved and in the crystalline states (tetragonal crystals, crosslinked by glutaraldehyde), were thus investigated in a variety of environmental conditions. The effect of a wide range of alcohols demonstrates that lysozyme, whether in solution or crystalline, displays structural features which are on the whole strikingly similar. By contrast, in the case of urea this similarity becomes apparent only for concentrations higher than 4 M. Molecular interpretation of the data, as discussed in the text, is entirely consistent with information from X-ray studies.

Alcohols↗
PubMed1976

Investigation of ribonuclease-catalysed kinetics by a micro-calorimetric method.

A rapid micro-calorimetric method for the simultaneous determination of the Michaelis-Menten parameters and the enthalpy of enzymic reactions is developed. The hydrolysis of 2': 3'-cyclic CMP by ribonuclease A is studied to test the proposed method; values obtained are in good agreement with already published data. Enzymic hydrolysis of yeast RNA, unlike that of cyclic phosphates, is shown to be endothermic. This result is explained by the two-step mechanism of this reaction.

Calorimetry↗
PubMed1975

Hydrogen ion titration of lysozyme in alcohol-water solutions.

H+ titration curves of hen egg-white lysozyme were obtained at 0.15 I in the presence of small amounts (less than 15%) of methanol, ethanol and n-propanol. The acidity constants of two groups (whose pK values in water are, respectively, 42 and 3.5) are increased in water-alcohol mixtures in comparison to water. From the evaluation of these constants as a function of alcohol concentration and hydrocarbon chain length, it is suggested that these alcohols interact specifically with lysozyme. As pK values of 4.2 and 3.5 in water are generally assigned to Asp-101 and Asp-52 respectively, it seems that interaction occurs within the active site of the enzyme.

1-Propanol↗