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Biomedical subjects

A Baudras

Publications and source records attributed to A Baudras.

11 recordsLinked to original sources
PubMed1992

Near ultraviolet circular dichroism study of the cyclic AMP receptor protein, its NH2-terminal domain and their interaction with cyclic AMP.

Circular dichroism in the near ultraviolet wavelength range was employed to examine conformational features of CRP (a dimer with a chain of 209 amino acids) and of its subtilisin core -alpha CRP- which retains the cAMP binding site (a dimer spanning the sequence 1-117). Binding of the ligand cAMP (allosteric activator), as well as cGMP was also investigated. The well resolved transitions could be assigned to the various classes of aromatic amino acid residues in the two proteins. In addition to signals which are attributable to the missing aromatic residues (Phe-136 and Tyr-206) the difference spectrum (CRP minus alpha CRP) shows a significant perturbation of a tryptophanyl contribution centred at 296 nm. From the available X-ray structure of the cAMP-CRP complex we are led to conclude that a conformational reorganisation takes place in the alpha CRP. A very large negative maximum is observed at 255 nm when cAMP binds to CRP and to alpha CRP. The maximum effect is observed in both cases at a ratio of one ligand bound per protomer. In the 280-300 nm wavelength range a smaller but significant perturbation affects specifically the spectra and reveals different cAMP-induced conformational changes in the two proteins. We propose that the major (255 nm) contribution to the perturbation spectrum of bound cAMP, and the qualitatively similar signal for cGMP, reflects an immobilisation of the sugar and adenine moieties of the bound ligand in an almost anti-conformation for both CRP and alpha CRP.

Bacterial Proteins↗
PubMed1979

Non-specific interactions of CRP from E. coli with native and denatured DNAs: control of binding by cAMP and cGMP and by cation concentration.

The cyclic adenosine 3',5'-monophosphate receptor protein of Escherichia coli (CRP) binds cooperatively to single- and double-stranded DNA. Binding data could be fitted to the model of McGhee and von Hippel (1) and show that neither strandedness of DNA, nor the effectors cAMP and cGMP or the ionic strength (KCl) do change appreciably the cooperativity parameter omega (omega approximately or equal to 100), and site size of DNA. Instead, distinctly different slopes were observed for the linear decrease of log K omega (a measure of the overall affinity) as a function of log (K+). From these double-log plots (2), the number of cations released and the non-electrostatic contributions to the binding free energy could be determined. Binding of CRP to single-stranded DNA is slightly favored under physiological ionic conditions (0.15-0.20 M), but such a preferential binding is almost abolished in the presence of cAMP which increases the strength of the interaction of the protein with both forms of DNA. CGMP does not change the binding properties and interactions of CRP with DNA. These observations do not support the proposal that the cAMP-CRP complex could stimulate transcription via some "melting" property unless its interactions be dramatically changed when it binds specifically to promoter DNA.

Bacteriophage lambda↗
PubMed1979

[Cooperative non-specific binding of the cyclic adenosine 3'--5'-monophosphate receptor protein (CRP) from Escherichia coli to double-stranded thymus and lambda pgal DNA].

Either free or combined with cAMP, CRP binds cooperatively to double-stranded thymus and lambda pgal DNA. The affinity of CRP for both DNAs in these non-specific interactions is increased by cAMP without noticeable change in the degree of cooperativity. Values of the intrinsic association constant, cooperativity parameter, and site size of DNA were determined from ultracentrifugal investigations under near-physiological ionic conditions.

Animals↗
PubMed1978

A fluorescence approach of the determination of translational diffusion coefficients of lipids in phospholipid monolayer at the air-water interface.

In the present work, it is shown that the photobleaching technique as well as experimentation based on fluorescence recovery after bleaching can be extended to monolayers spread at the air-water interface. A mathematical model is derived which allows the determination of translational diffusion coefficients of species diffusing in such a system. Using 12-(9-anthroyl)stearic acid (anthroylstearate) as a fluorescent probe, dispersed either in dipalmitoylphosphatidylcholine or in dipalmitoylphosphatidylglycerol in various conditions of subphase ionic composition and surface pressure of the monolayer, including phase transition domains, we are led to the following conclusions: 1. Anthroylstearate molecules seem to aggregate in 'microdomains' where their fluorescence properties remain unchanged regardless of the compression states of the host monolayer. 2. In any case, a break in the diffusion constants appears on compressing films of both dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol. In particular, this break coincides with the liquid expanded to gel phase transition of these lipids when it occurs. 3. Diffusion of anthroylstearate in dipalmitoylphosphatidylglycerol depends strongly on the subphase ionic strength and on the nature of cations: Na+, Mg2+, Ca2+.

Diffusion↗
PubMed1977

A fluorescence study of the binding of cytochrome C to mixed-phospholipid microvesicles : evidence for a preferred orientation of the bound protein.

Kinetic and equilibrium experiments are reported on the binding of the fluorescent probe 1,8-anilino-naphtalene sulfonate (ANS) to microvesicles of natural lecithin containing 10 per cent of an anionic phospholipip (90 : 10 mixtures). Kinetics discriminated between fast binding to the outer leaflet of the bilayer and apparently slow binding to the inner leaflet controlled by the diffusion of the probe across the bilayer. The equilibrium distribution of ANS between the two leaflets was not dependent on the nature of the anionic species and the spectral properties of bound ANS were identical in all cases investigated. A hyperbolic saturation was observed allowing to propose an affinity scale for the binding of ANS to mixtures of lecithin with phosphatidic acid, phosphatidylinositol, and cardiolipin. The effects on binding of ionic strength and sodium dodecylsulfate were also considered. The binding of horse heart ferricytochrome c to ANS-labelled microvesicles was studied quantitatively making use of the quenching of the probes fluorescence by the heme. Perrin-Förster energy transfer could be analysed on the basis of a simple model of the physical arrangement of the system which was elaborated from published data referring to ANS and cytochrome c binding to phospholipids. Experimental and theoretical computed values of the quenching efficiency were compared and led to conclude in favor of a preferred orientation of the heme crevice fully accessible from the external space at the lipid interface.

Anilino Naphthalenesulfonates↗
PubMed1976

Mechanism of yeast cytochrome b2 action. I. Thermodynamics and relaxation kinetics of the interaction between cytochrome b2 and oxalate.

Oxalate is the strongest known inhibitor of yeast cytochrome b2 activity. We have used spectrophotometric titration, temperature-jump relaxation, and calorimetry in an investigation of the interaction between enzyme and inhibitor. The titration data are consistent with noncooperative binding to one site per subunit. This conclusion is corroborated by temperature-jump results which reveal a single relaxation phenomenon which obeys second-order kinetics. Further evidence for a simple binding reaction enthalpy estimated from relaxation amplitudes is in good agreement with the value obtained directly with batch calorimetry. The forward and reverse rate constants evaluated from the temperature-jump experiments are, respectively, 1 x 10(4) M-1 sec-1 and 15 sec-1. Although considerably smaller than a diffusion-controlled value, the forward rate constant is characterized by an unusually small activation energy of approximately 3 kcal/mol. This, together with a large unfavorable association activation entropy of -30 eu, suggests that oxalate diffuses freely to the active site, but only a small fraction of the collisions are productive due to severe steric requirements.

Binding Sites↗
PubMed1976

Mechanism of yeast cytochrome b2 action. II. Steady-state kinetics of oxalate inhibition.

From a careful steady-state kinetic study it is shown that the inhibition of L-lactate oxidation by cytochrome b2 with ferricyanide as acceptor is of the mixed competitive-noncompetitive type, indicating the formation of an active ternary complex between enzyme, substrate, and inhibitor. With a large excess of acceptor, the simplest formal mechanism consistent with all available data is: E + L equilibrium EL; E + S equilibrium ES leads to EP leads to E + P; ES + L equilibrium ESL leads to EPL leads to EL + P, where L is oxalate, S is L-lactate, P is pyruvate, and E is enzyme. The inhibition kinetics together with the rate constants for oxalate binding to free enzyme (Thusius, D., Blazy, B., and Baudras, A. (1976), Biochemistry, preceding paper in this issue) and recent steady-state experiments on L-lactate deuterated at C-2 (Lederer, F. (1974), Eur. J. Biochem, 46, 393) lead to estimates of some of the elementary rate parameters in the above scheme. As in the case of oxalate (see Thusius et al. reference above), the association rate constant for substrate binding (1.1 x 10(5) M-1 sec-1) is much smaller than a diffusion-controlled value. Our results also imply that dissociation of complex EP to free enzyme and pyruvate is partially rate limiting for the overall reaction.

Binding Sites↗
PubMed1976

Spectrophotometric and electrochemical determinations of L(+)-lactate in blood by use of lactate dehydrogenase from yeast.

Lactate can be determined rapidly in blood by spectrophotometric and amperometric (enzyme electrode) procedures based on its oxidation by ferricyanide, the reaction being catalyzed with yeast L(+)-lactate dehydrogenase (cytochrome b2) (EC 1.1.2.3). In the photometric method lactate can be measured in a few minutes, but blood samples must first be deproteinized. In the amperometric procedure no treatment of blood is needed except ferricyanide addition. The enzyme electrode we used has a response time shorter than 1 min when its critical variables are optimized. Preliminary standardization is reduced to minimum operation, because electrode response is proportional to lactate concentration over a wide range (0.1 to 8.0 mol/liter) and many determinations can be done with little cost in enzyme. A simple electrical device ("two-electrode device") is described that is well suited for furture micro-cell construction. Lactate determinations on a series of normal blood samples show no deviation between results by these new methods and the usual ultraviolet spectrophotometric lactate tests.

Animals↗