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Biomedical subjects

P Dessen

Publications and source records attributed to P Dessen.

71 records · Page 4Linked to original sources
PubMed1976

Methionyl-tRNA synthetase from Escherichia coli: active stoichiometry and stopped-flow analysis of methionyl adenylate formaiton.

Native dimeric methionyl-tRNA synthetase and its monomeric proteolytic fragment are shown to form and to bind 1 mol of methyionyl adenylate per polypeptide chain. Moreover, at 25 degrees C, each monomer of the dimeric native enzyme behaves independently, exhibiting the same parameters for the methionine activation reaction as does the monomeric modified enzyme. These results were obtained using several independent methods including equilibrium and nonequilibrium dialysis, active site and tryptophan fluorescence titrations, and stopped-flow by fluorescence. Stopped-flow resolution of the reversible methionine activation reaction also demonstrates that methionine and ATP-Mg2+ react without coupling to form a ternary enzyme-methionine-ATP-Mg2+ complex. This complex readily converts to enzyme-methionyl approximately adenylate-PP-Mg2+ with a standard free energy close to zero. It is concluded that the uncoupled enzyme-methionine-ATP-Mg2+ complex may resemble the transition state of the reaction at the expense of the additional state of the reaction at the expense of the additional synergistic binding energy provided by reciprocal coupling, within the site, of the methionine molecule with the adenosine and PP-Mg2+ parts of the ATP-Mg2+ molecule (Blanguet, S., Fayat, G., and Waller, J. P. (1975), J. Mol. Biol. 94, 1.).

Adenosine Monophosphate↗
PubMed1976

Interactions of oxytocin and vasopressin with bovine neurophysins I and II. Effects of hormone binding on the protein quaternary structure: a simple model.

The effects of hormone binding on the reversible monomer in equilibrium dimer equilibrium of bovine neurophysins I or II in solution have been studied by sedimentation equilibrium measurements performed in conjunction with equilibrium dialysis experiments. Under normal solution conditions saturating amounts of oxytocin displace the neurophysin dimerization equilibrium toward the associated form of the protein to give a dimeric complex with two oxytocin molecules bound per dimer. Vasopressin exerts different influences on this oligomerization process. At low fractional saturation this ligand exhibits a behavior similar to oxytocin with a higher affinity for the neurophysin dimer than the monomer. But in contrast, at higher fractional saturation, vasopressin strongly displaces the aggregation equilibrium toward a monomeric complex bearing two vasopressin molecules. However, in the presence of a high concentration of LiCl two oxytocin molecules are bound per neurophysin protomer (10,000 daltons). These observations, together with earlier data for vasopressin binding, suggest that each neurophysin molecule possesses two structurally distinct hormone binding sites. These observations can be rationalized in a simple schematic model of hormone binding to neurophysin in which oxytocin favors a dimeric form with one hormone binding site available per 10,000 daltons while vasopressin favors the monomeric form with two hormone binding sites available per 10,000 daltons.

Animals↗
PubMed1976

Small-angle x-ray and light-scattering study of native and trypsin-modified methionyl-tRNA synthetase from Escherichia coli.

Small-angle X-ray scattering experiments were performed on an absolute scale on solutions of methionyl-tRNA synthetase from Escherichia coli in its native and trypsin-modified forms. A light-scattering study was performed on the same solutions to verify monodispersity. The structural parameters for the trypsin-modified enzyme, radius of gyration (2.48 nm), volume (90 nm3), surface/volume (1.5 nm-1) and the distribution of chords can account for an equivalent prolate ellipsoid of revolution having an axial ratio 2.3 and a maximum length of 9 nm, with a creviced surface. The rsults obtained for the native enzyme [i.e. radius of gyration (4.3 nm), volume (244 nm3), distribution of the scattering intensity and distribution of chords] exclude the possibility of a very compact quaternary structure and suggest that the enzyme consists of at least two globular parts, probably the two protomers, linked together by interactions involving a limited region of the structure.

Amino Acyl-tRNA Synthetases↗
PubMed1976

A computer simulation of the effect of injected anti-progesterone on progesterone levels of pregnant rats.

Antibodies to progesterone injected into pregnant rats, provoke abortion if the concentration of the biologically active progesterone is reduced to a critical level. By stimulating the biological experiments in the computer we describe the time dependent changes of this progesterone fraction, as a function of the initial concentration of progesterone and of the anti-progesterone injected. Results obtained can be used to aid interpreting the findings of the biological studies and to calculate the concentration of anti-progesterone required to provoke abortion.

Abortion, Induced↗
PubMed1976

The parameters of the binding of estradiol and progesterone to their antibodies in presence of rat plasma.

The binding of estradiol and progesterone to the corresponding antibodies has been studied in system containing : a) antibody and hormone or b) antibody, hormone and rat plasma. In sytem a) the apparent association constant and the concentration of the antibody have been determined and the optimal conditions of a standard antibody-assay have been elaborated. In system b) the specific binding of hormone to antibody in presence of rat plasma has been measured, and the value of the "Operational Association Constant", Kop, has been calculated. Kop has the dimensions of an apparent association constant : it defines the ratio hormone bound/unbound to antibody, as a function of hormone concentration in system b). Based upon these experiments, the extent of hormone-binding to antibody injected to rats can be predicted. When antibody and hormone concentrations are measured in the plasma, the concentrations of hormone bound to antibody can be calculated.

Animals↗