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J C Vincent

Publications and source records attributed to J C Vincent.

28 records · Page 2Linked to original sources
PubMed1983

Theoretical analysis of the significance of whether or not enzymes or transport systems in structured media follow Michaelis-Menten kinetics.

Pure Michaelis-Menten enzymes have been studied (i.e., enzymes with a hyperbolic (S, V) behavior in a well-stirred solution). When such enzymes are associated with a structure in vitro, even in the simplest conceivable form (immobilization in a homogeneous gel), they can produce enzymic or transport reactions with many different kinetics (Michaelis-Menten, sigmoidal, dual-phasic, etc.). Therefore, when structured enzyme or transport processes in vivo have sigmoidal kinetics, it is not proof that the corresponding proteins are allosteric. In same manner, when the apparent kinetics are dual-phasic, it is not proof that two enzyme, or transport systems, coexist.

Biological Transport↗
PubMed1982

Monitoring of artificial enzyme membrane systems by electric currents. I. Analytical treatment with direct current and buffered conductivity.

Continuous electric fields (E) modify the transport flows and the intramembrane concentration profiles of protons or of ionic substrates or cofactors (inhibitors). These "mediators' induce variations in enzyme activity, quantifiable by a generalized Damköhler group II psi distinguishing electrotransport reactions from diffusion reactions. For three typical reaction schemas, using only one mediator, the steady-state equations have been established. Depending on boundary conditions, the direction of electric current (for asymmetrical systems) and the value of psi, activations, inhibitions or activations followed by inactivations have been found. With buffered conductivity (supporting electrolyte), the limiting concentration profiles (E leads to infinity) are uniformly equal to the boundary values; i.e., diffusion constraints are suppressed and the regime is controlled by the reaction. The calculations give the relative activity variations for partially suppressed transport controls.

Biological Transport↗
PubMed1981

[Temporal oscillations in a structured enzymatic medium. Vectorial transport with space-time oscillations Analytic study].

An analytical diffusion-reaction model of chemical time-oscillations is obtained with two Michaelian enzymes and boundaries selectively open to H+ or OH- ions. One reaction produces, and the other one consumes H+ ions. During a half oscillation the high reaction rate is progressively equalled by the rate of diffusion, the substrate is consumed and diffusion through the boundaries brings the pH back toward its original value. Asymmetrical selectivities on the boundaries lead to a new "time oscillatory vectorial transport model".

Biological Transport, Active↗
PubMed1981

Two-enzyme active transport in vitro with pH induced asymmetrical functional structures. III. Discussions based on numerical treatments of the time-dependent evolutions.

Three complementary models have been considered in which pH gradients (step function, linear pH or linear H+) impose asymmetry on a two-enzyme mixture. If the "combined pH dependences" of enzymes is pro-asymmetrical, the pH gradient induces an asymmetrical distribution of potential activities ("latent" asymmetry of functional structure). When substrate is added, "developed" asymmetry of effective activities appears which results in "substrate space wave" and pumping when the catalysed reaction couple is "inversible". It is shown that only one steady state exists for a given boundary condition and is attained when the "combined effective activity" of enzymes is nil; the stationary flux with symmetrical boundaries or the stationary load with moving boundaries is proportional to "effective global activities" of enzymes. "Equivalent square models" could be proposed that would be able to describe "functional" or "permanent" structure pumps as well. These models belong to the thermodynamic branch and the asymmetrical "space wave" substrate concentration profiles obtained must be distinguished from dissipative structures. It appears that such primary active transport pumps are chemical equivalents of heat pumps.

Biological Transport, Active↗
PubMed1977

[Regulation and electric excitation of enzyme membranes in vitro].

Enzyme membranes can be activated or inhibited by applying continuous or alternating electrical fields. The field can modify the transport or reaction term of the transport-reaction by action on the displacement of charged species including those giving pH effects or inducing volume flows. A first experimental example is given: the progressive supression of the inhibition of hexokinase by the product when increasing alternating fields are applied. In the same way the apparent optimal pH approaches that of the soluble enzyme. In addition to its theoretical and practical implications electrical regulation can lead to the monitoring of enzyme reaction-driven mechanochemical fibers.

Electric Stimulation↗
PubMedDate not supplied

Hypothesis: hyperstructures regulate bacterial structure and the cell cycle.

A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructure's enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle.

Bacteria↗