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A Friboulet

Publications and source records attributed to A Friboulet.

32 records · Page 2Linked to original sources
PubMed1988

Electrical excitability of artificial enzyme membranes. IV. Theoretical approach of the membrane potential of synthetic proteinic films.

This paper deals with the theoretical approach of the membrane potential of artificial proteinic film. Programming techniques using finite difference simulations for the steady state and transient solutions of the Nernst-Planck and Poisson equations were used and solved by the collocation and corrector methods. This approach allows one to calculate the membrane potential without any discontinuity between the Donnan and the diffusion potentials, the thickness of the boundary layers being automatically determined by the intrinsic properties of the solution and of the membrane. The theoretical results are compared with experimental potentials measured on proteinic artificial films.

Enzymes↗
PubMed1987

Substrate activation and thermal denaturation kinetics of the tetrameric and the trypsin-generated monomeric forms of horse serum butyrylcholinesterase.

Native horse serum butyrylcholinesterase (acylcholine acylhydrolase; EC 3.1.1.8) is a tetrameric enzyme which can dissociate after a limited proteolysis by trypsin into three additional molecular forms, including the monomeric entity. The trypsin-generated monomer of butyrylcholinesterase, isolated by ultracentrifugation on sucrose gradient, is stable and allows the relations between the polymeric structure of butyrylcholinesterase and its kinetic characteristics to be approached, e.g., substrate activation and complex thermal denaturation curves. The trypsin-generated monomer of butyrylcholinesterase behaves with identical kinetic parameter values as the native tetrameric enzyme. On the other hand, the thermal denaturation of the native tetrameric butyrylcholinesterase does not follow first-order kinetics, but may be described by a sum of exponential terms. This behavior is not due to the polymeric nature of butyrylcholinesterase but seems to be related to a structural heterogeneity induced by the heat treatment.

Animals↗
PubMed1987

Horse serum butyrylcholinesterase kinetics: a molecular mechanism based on inhibition studies with dansylaminoethyltrimethylammonium.

The kinetics of the hydrolysis of butyrylthiocholine by horse serum butyrylcholinesterase (acylcholine acylhydrolase; BuChE; EC 3.1.1.8) exhibit an activation phenomenon at high substrate concentrations. At least two mechanistic models can account for the enzyme kinetics: one assumes the binding of an additional substrate molecule on the acyl-enzyme intermediate, and the other hypothesizes the existence of a peripheral regulatory site for the substrate. (1-Dimethylaminonaphthalene-5-sulfonamidoethyl)-trimethylammonium perchlorate, a potent reversible inhibitor, appears to affect BuChE activity by binding to a peripheral site. The inhibition is of the mixed type at low substrate concentrations and of the competitive type at high substrate concentrations. This is consistent with a peripheral site for the binding of the substrate responsible for the activation phenomenon.

Animals↗
PubMed1985

Rapid changes in levels of individual molecular forms of acetylcholinesterase after denervation of mouse sternocleidomastoid muscle.

Experimental denervation of adult mouse sternocleidomastoid muscle results in a decrease in total AChE. The most rapid change essentially affects the tailed, asymmetric 16 S AChE, since one day after nerve section, "16S" AChE is already significantly decreased to about 70% of its control value. We found that both background and junctional "16S" AChE are affected by this rapid decrease. Later, a sharp fall in "10S" and "4S" AChE occurs about seven days after denervation when muscle atrophy develops with loss of weight and proteins. A gaussian analysis of the sedimentation profiles of AChE extracted from denervated muscle shows that there is not only an early rapid decrease in 16 S AChE but also a decrease in the monomeric 3.3S AChE. This result suggests that there is a very rapid turn-over of two molecular forms of AChE, the supposedly monomeric precursor and the complex asymmetric 16S AChE.

Acetylcholinesterase↗
PubMed1984

Polymorphism of acetylcholinesterase and identification of new molecular forms after sedimentation analysis.

Acetylcholinesterase (AChE) is composed of several distinct molecular forms, which are identified and partly resolved by velocity sedimentation analysis on sucrose gradients. We made the assumption that each AChE form sediments as a peak of activity with a gaussian shape in the continuous sucrose gradient. We experimentally demonstrate that the complex AChE profiles can be decomposed in gaussian distributions of separate molecular entities. We performed a high salt-detergent extraction of AChE from mouse skeletal muscle and isolated fractions enriched in each particular from. These fractions were then submitted to a second sedimentation, to assess the stability and to further characterize each AChE form. Then, we calculated the statistical significance level of each AChE form and identified up to 9 separate molecular specifies in mouse adult muscle. These forms are the major "4 S", "6.5 S", "10 S", "12 S" and "16 S" and minor molecular active components of AChE. These results suggest complex structural interactions between catalytic and non catalytic subunits of AChE and do not simply fit the tailed asymmetric globular model of AChE with six molecular species.

Acetylcholinesterase↗
PubMed1982

Electrical excitability of artificial enzyme membranes. I. Ion-exchange properties of synthetic proteinic films.

This paper deals with the physico-chemical properties of artificial membranes. The membranes are produced with different protein molecules which offer amphoteric sites with weakly ionizable groups. The adsorption of phosphate and sodium ions in different artificial proteinic membranes is studied as a function of both pH and concentration of the external solution. The influence of the sign and density of fixed charges as the nature and concentration of mobile ions is studied by measuring the potential difference between both membrane compartments.

Acetylcholine↗
PubMed1982

Electrical excitability of artificial enzyme membranes. II. Electrochemical and enzyme properties of immobilized acetylcholinesterase membranes.

This paper deals with aspects of the reciprocal interaction between enzyme activity and the microenvironment or the potential difference in artificial proteinaceous membranes bearing cross-linked acetylcholinesterase. The potential difference resulting from asymmetric substrate injection into the system is recorded as a function of time. The influence of the membrane charge density on both enzyme activity and potential difference is studied by varying the external solution pH. The enzyme specific potential is initiated by local change of pH at the membrane level and the dependence on the buffer strength is studied. The recorded potential difference appears to be the result of the reciprocal interaction between enzyme reaction and the diffusion of substrate or products.

Acetylcholinesterase↗
PubMed1982

Electrical excitability of artificial enzyme membranes. III. Hysteresis and oscillations observed with immobilized acetylcholinesterase membranes.

Experimental evidence for memory and oscillations in artificial acetylcholinesterase membranes is presented. When acetylcholine is injected on one side of an artificial proteinic membrane bearing acetylcholinesterase, a potential difference is recorded as a function of time. The steady-state potential due to the enzyme activity for increasing and decreasing substrate concentrations exhibits a hysteresis loop. The non-linearity of the enzyme reaction coupled with the diffusion constraints cause also some instabilities, such as oscillations of the membrane potential.

Acetylcholinesterase↗
PubMedDate not supplied

Abzyme generation using an anti-idiotypic antibody as the "internal image" of an enzyme active site.

Since the two reports published in 1986 by the laboratories of R. Lerner and P. G. Schultz, it has been clearly established that antibodies may be induced to act as catalysts in numerous chemical reactions. In all cases, catalytic antibodies were elicited using a substrate-based approach. In the present article, we propose an alternative and complementary enzyme-based approach to generate catalytic antibodies. This approach uses the properties of anti-idiotypic antibodies to generate internal images of enzyme active sites. Experimental results are discussed for polyclonal and monoclonal anti-idiotypic antibodies.

Acetylcholinesterase↗
PubMedDate not supplied

[A structure-activity study of a catalytic antiidiotypic antibody to the human erythrocyte acetylcholinesterase].

The catalytic monoclonal antibody 9A8 (MA 9A8), antiidiotypic to the antibody AE-2 (MA AE2) produced to the active site of acetyl cholinesterase from human erythrocytes, was subjected to a structure-function study. The specific binding of MA 9A8 to MA AE2 (K 2.26 x 10(9) M-1) was shown by the method of surface plasmon resonance, and the functional activity of MA 9A8 was demonstrated. Unlike acetyl cholinesterase, this antibody specifically reacted with the irreversible phosphonate inhibitors of esterases. A peptide map of MA 9A8 was analyzed by MALDI mass spectrometry. The Ser99 residue of its heavy chain was shown to be within the active site of the catalytic antibody. A computer modeling of the MA 9A8 active site suggested the existence of a catalytic dyad formed by Ser99 and His35. A comparison of the tertiary structures of the MA 9A8 and the 17E8 monoclonal antibody, which also exhibited an esterase activity and was produced to the stable analogue of the reaction transition state, indicated a practically complete coincidence of the structures of their presumed active sites.

Acetylcholinesterase↗
PubMedDate not supplied

Catalytic mechanism of an abzyme displaying a beta-lactamase-like activity.

A catalytic IgG (Ab2) displaying a beta-lactamase-like activity was previously obtained by using the antiidiotypic pathway: the particularity of this antibody is that it is a true antiidiotype of the beta-lactamase active site. We have previously demonstrated that this IgG has retained some of the structural information displayed by the beta-lactamase active site, evident from data that polyclonal anti-Ab2 antibodies (Ab3) recognize beta-lactamase. In this article, we investigated the catalytic mechanism of the abzyme compared to that of the enzyme. The experimental data allow us to hypothesize the catalytic residues required for catalysis.

Animals↗