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Biomedical subjects

J Janin

Publications and source records attributed to J Janin.

At least 109 records · Page 6Linked to original sources
PubMed1980

Analytical approximation to the accessible surface area of proteins.

We propose an analytical substitute to the geometrical construction that is commonly used in calculating the protein surface area that is accessible to the solvent. A statistical approach leads to an expression of accessible surface areas as a function of distances between pairs of atoms or of residues in the protein structure, assuming only that these atoms or residues are randomly distributed in space but not penetrating each other. This function gives good estimates of the accessible surface area and of the area buried in subunit contacts for a number of proteins. Its evaluation is very fast, and the function can be differentiated, which opens the way to new applications of accessibility measurements in the study of proteins. As an example, we show that the presence of domains is easily detected by an automatic procedure based on surface areas only.

Journal Article↗
PubMed1980

Relationship between hemoglobin A1c and insulin C-peptide in anomalies of carbohydrate metabolism.

In this paper, we have compared the results obtained for hemoglobin A1c and C-peptide concentrations, was not convenient for the diagnosis of anomalies in the regulation of carbohydrate metabolism in obesity or in latent diabetes. Nevertheless, hemoglobin A1c allowed us to check carbohydrate metabolism and to discriminate diabetes treated by oral therapy from insulin dependent diabetes; in these latter cases, hemoglobin A1c concentration varied inversely as C-peptide concentration as it was shown by the method of factor analysis in particular "principal components analysis". In the control of insulin dependent diabetes in a remission, hemoglobin A1c allowed assessment of the regulation of carbohydrate metabolism after suppression of insulin therapy. Thus, hemoglobin A1c is an index of the adaptation of insulin secretion in anomalies of carbohydrate metabolism.

C-Peptide↗
PubMed1978

Role of hydrophobicity in the binding of coenzymes. Appendix. Translational and rotational contribution to the free energy of dissociation.

We calculate the loss of surface area accessible to solvent associated with coenzyme binding in Clostridium flavodoxin, in dogfish lactate dehydrogenase, and in lobster glyceraldehyde-3-phosphate dehydrogenase. The coenzymes are nearly buried in the complexes and lose on the order of 600 A2, while the proteins lose a similar amount of accessible surface area. Some of the loss can be attributed to conformation changes in the protein, at least in the case of lactate dehydrogenase, where we show that the apoenzyme has a larger accessible surface area than the holoenzyme. Using known correlations with the hydrophobic contribution to the free energy, we demonstrate that hydrophobicity is the major source of stabilization free energy in FMN binding to flavodoxin and in NAD binding to the two dehydrogenases: it contributes 25 to 30 kcal/mol to the free energy of dissociation, more than required in order to compensate for the loss of six degrees of translational/rotational freedom by the coenzyme.

Animals↗
PubMed1976

Role of subunit interfaces in the allosteric mechanism of hemoglobin.

We calculate the surface area buried in subunit interfaces of human deoxyhemoglobin and of horse methemoglobin. A larger surface area is buried in deoxy- than in methemoglobin as a result of tertiary and quaternary structure changes. In both molecules the dimer-dimer interface is closepacked. This implies that hydrophobicity stabilizes the deoxystructure, the free energy spent in keeping the subunits in a low-affinity conformation being compensated by hydrophobic free energy due to the smaller surface area accessible to solvent.

Allosteric Regulation↗
PubMed1975

Principles of protein-protein recognition.

The formation of the protein-protein interface by the insulin dimer, the trypsin-PTI complex and the alphabeta oxyhaemoglobin dimer removes 1,130-1,720 A2 of accessible surface from contact with water. The residues forming the interface are close packed: each occupies the same volume as it does in crystals of amino acids. These results indicate that hydrophobicity is the major factor stabilising protein-protein association, while complementarily plays a selective role in deciding which proteins may associate.

Animals↗
PubMed1975

[Radiocrystallographic analysis of protein structures].

General description of X-ray diffraction by single crystals : Bragg's law, reciprocal lattice and Ewald's construction, structure factors. Role of resolution in protein structure determination. Fourier transform relations between structure factors and electron density maps. Phase determination using isomorphous replacement. Interpretation of electron density maps : building protein atomic models, their use in biochemistry.

Crystallography↗