Experimental and theoretical studies of membrane oscillations
Abstract
Experimental and theoretical studies of oscillations and chaos in artificial membranes which mimic some biological systems are carried out. Polystyrene sulfonate membranes were studied to determine whether this membrane system can mimic an ion gate and will exhibit oscillatory behavior. Blockage of the membrane pores due to the adsorption of PSS depends on the MW of the PSS, the type of membrane filter and the ionic strength of the solution. Aperiodic oscillations in membrane potential in a DOPH Millipore filter were obtained and analyzed for the existence of deterministic chaos using standard methods from nonlinear dynamics theory. Reliable values of the correlation dimension and Lyapunov exponent can be obtained if the dependence on important parameters is treated carefully; the resulting correlation dimension and Lyapunov exponent values are, indeed, indicative of chaos in this system. Membranes made by immobilizing acetylcholinesterase in bovine serum albumen were prepared and studied. The potential across the membrane was measured when the substrate, acetylcholine, was introduced into one side of the diffusion cells. The activity and the amount of the enzyme as well as the thickness of the membranes can be reflected by the measured potentials. This provides a new way to determine the kinetics of enzyme reactions. Two chemical kinetic models are investigated using standard nonlinear dynamics techniques to determine the conditions under which substrate inhibition kinetics can lead to oscillations, in particular, in a model of an immobilized enzyme membrane. The first model is a classical substrate inhibition scheme based on Michaelis-Menten kinetics and involves a single substrate. Only when this reaction takes place in a flow reactor are oscillations observed. A second model is based on a general mechanism applied to the kinetics of many pH-dependent enzymes which includes both substrate inhibition kinetics as well as autocatalysis through the activation of the enzyme by hydrogen ion. The autocatalysis is always responsible for oscillatory behavior in this scheme. The substrate inhibition terms affect the steady state behavior but do not lead to oscillations unless product inhibition is present.
Degree
Ph.D.
Advisors
Larter, Purdue University.
Subject Area
Chemistry|Biophysics
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