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Biomedical subjects

W R Vieth

Publications and source records attributed to W R Vieth.

At least 19 recordsLinked to original sources
PubMed1992

Transport regulation of recombinant gene expression in E. coli and B. subtilis.

Expression kinetics of the lactose (lac) operon in Escherichia coli are reviewed for both wild-type and recombinant cell cultures under chemostatic conditions. A unified model which involves regulation of active inducer (lactose) transport, promoter-operator regulated expression of the lac operon, glucose-mediated inducer exclusion, and catabolite repression is summarized and supporting data is shown to verify its accuracy. The synthesis of alpha-amylase with a recombinant form of Bacillus subtilis is also reviewed to point out generic features in transport regulation, the lac operon model providing a point of departure. While there are many similarities in the influence of transport on both regulating models, there are also important differences. In a chemostat system, the synthesis of alpha-amylase is nongrowth associated, while beta-galactosidase is a growth-associated enzyme. Nevertheless, transport regulation is an important feature in both instances.

Journal Article↗
PubMed1984

Transport of acetylcholine in a membrane. Laminate model of the neuromuscular junction.

A laminate model of the cleft-plus-postsynaptic membrane structure of the neuromuscular junction was studied. In order to prepare a model of the postsynaptic membrane, the properties of acetylcholine (Ach) receptor-rich vesicles purified from Torpedo fish were measured. Immobilization of vesicles was demonstrated by various methods, in particular, by investigating collagen and carrageenan matrices as models of the fluid-filled fibrous matrix of the cleft. It was found that a laminated system employing a liquid membrane-containing vesicle suspension, together with a swollen collagen membrane, is an appropriate model for examining important transport/reception aspects of the cleft-plus-postsynaptic membrane structure. Combined transport with immobilization of Ach in the liquid membrane system was elucidated and effective diffusivities in the vesicle suspension layer were calculated. Effective diffusivities of the composite system simulating the cleft and the postsynaptic membrane were evaluated as well. These data illustrate the importance of penetrant immobilization in retarding the diffusion process during neurotransmission.

Acetylcholine↗
PubMed1983

Diffusional/kinetic analysis of the neurotransmission process at the nerve-muscle junction.

Transmission at the neuromuscular junction is known to comprise the following steps: vesicular release of Ach pulses; transport across the synaptic cleft; partial hydrolysis by Ach-ase; binding to Ach receptors; ion channel opening and closure, and, thereby, alteration of sodium and potassium conductances. Combining these elements, a unified model has been constructed that is effective in describing the relation between neurotransmitter arrival at receptor sites and channel openings, leading to simple relationships for sodium and potassium conduction at the neuromuscular junction. Application of the model to mepc and epp data has been successful.

Animals↗
PubMed1981

Transport models of the neurotransmitter-receptor interaction.

Recently, in membrane transport studies, we have observed the duality of ligand-binding site interactions in a structural protein membrane. Separately, the role of membrane anisotropy in the transport/catalytic behavior of an enzyme-membrane was investigated and modeled by the present authors. In this work, we are combining the ideas of duality and anisotropy in a diffusional analysis of the phenomenon of migration of the neurotransmitter species acetylcholine (ACh) in the post-synaptic region of the neuromuscular junction. Employing the principle of mass conservation, a transient diffusion equation was formulated for ACh migration in this region; it was solved by numerical computation for the appropriate boundary conditions. Concentration profiles were generated and, with the aid of a simple linear coupling expressing regulation of the ion channel function by the ACh species bound to receptor sites in the active conformation, successful simulations of the nerve-muscle end-plate potential were obtained. Two subcases were considered: (a) static unilayer diffusional zone or "membrane." (b) moving active layer (multilayer or envelope membrane). Both models are capable of closely matching the normalized concentration profiles of the actively bound neurotransmitter species to the profile of normalized end-plate potential in reduced scale. A transport basis for the familiar two-state receptor-transmitter interaction is demonstrated and a plausible explanation of the role of geometry of the synaptic cleft and the function of junctional cholinesterases is provided. Arguments utilizing results from the literature, together with our simulation results, are employed in critical reexamination of the key concepts (diffusion, duality, anisotropy) and their validity is strengthened.

Biological Transport↗
PubMed1978

Modeling the role of cyclic AMP in catabolite repression of inducible enzyme biosynthesis in microbial cells.

Modeling the role of cyclic AMP (cAMP) in catabolite repression of inducible enzyme production in microbial cells was studied. A catabolite repression index, F, was defined based on the postulation that complex formation occurs between RNA polymerase (RNAP) and DNA, and shifting from the inert form to the open form of this complex (the latter form is required for transcription) is accelerated by the cAMP.CRP complex. The catabolite repression index, F, was incorporated into model equations of mRNA production. Empirical relationships between intracellular cAMP level and medium glucose concentration were established based on experimental data and introduced into the model. Computer simulation results were obtained for a number of interesting cases. The practical utility of the proposed model was demonstrated by comparing it with the experimental results on glucose isomerase biosynthesis.

Bacteria↗