ABSTRACT
When n types of univalent ligands are competing for the binding to m types of protein sites, the determination of the system composition at equilibrium reduces to the solving of a non-linear system of n equations in C = [0; 1](n). We present an iterative method to solve such a system. We show that the sequence presented here is always convergent, regardless of the initial value in C. We also prove that the limit of this sequence is the unique solution in C of the non-linear system of equations.
Subject(s)
Models, Biological , Proteins/metabolism , Algorithms , Binding Sites , Binding, Competitive , Blood Proteins/metabolism , Hormones/metabolism , Humans , Kinetics , Ligands , Protein BindingABSTRACT
The regulation of cellular function is often controlled at the level of gene transcription. Such genetic regulation usually consists of interacting networks, whereby gene products from a single network can act to control their own expression or the production of protein in another network. Engineered control of cellular function through the design and manipulation of such networks lies within the constraints of current technology. Here we develop a model describing the regulation of gene expression and elucidate the effects of noise on the formulation. We consider a single network derived from bacteriophage lambda and construct a two-parameter deterministic model describing the temporal evolution of the concentration of lambda repressor protein. Bistability in the steady-state protein concentration arises naturally, and we show how the bistable regime is enhanced with the addition of the first operator site in the promotor region. We then show how additive and multiplicative external noise can be used to regulate expression. In the additive case, we demonstrate the utility of such control through the construction of a protein switch, whereby protein production is turned "on" and "off" by using short noise pulses. In the multiplicative case, we show that small deviations in the transcription rate can lead to large fluctuations in the production of protein, and we describe how these fluctuations can be used to amplify protein production significantly. These results suggest that an external noise source could be used as a switch and/or amplifier for gene expression. Such a development could have important implications for gene therapy.
Subject(s)
DNA-Binding Proteins , Gene Expression Regulation, Viral , Repressor Proteins/genetics , Viral Proteins/genetics , Models, Genetic , Viral Regulatory and Accessory ProteinsABSTRACT
Stochastic noise of an appropriate amplitude can maximize the coherence of the dynamics of certain types of excitable systems via a phenomenon known as coherence resonance (CR). In this paper we demonstrate, using a simple excitable system, the mechanism underlying the generation of CR. Using analytical expressions for the spectral density of the system's dynamics, we show that CR relies on the coexistence of fast and slow motions. We also show that the same mechanism of CR holds in the oscillatory regime, and we examine how CR depends on both the excitability of the system and the nonuniformity of the motion.
ABSTRACT
Se presenta la experiencia de una Unidad de Reanimacion Digestiva a traves de 2 anos de actividad, de 32 enfermos sometidos a Reanimacion Enteral y que configuran 16.968 horas de atencion por bomba de alimentacion.Se analizan diferentes aspectos de la casuistica y se discuten los resultados con particular referencia a los fracasos concluyendo que los mismos son evitables en parte y no atribuibles a la RNM por otra
Subject(s)
Enteral Nutrition , Hospital UnitsABSTRACT
A preliminary communication on the excellent results of a new intraluminal prosthesis for palliative intubation of advanced oesophageal of cardial carcinoma is reported. Such prothesis includes an original and effective device to avoid gastro-oesophageal reflux and the ensuing peptic oesophagitis. Piloroplasty is considered convenient as an adjuvant in the prevention of gastro-oesophageal reflux.
