Structural Kinetic Model Research Articles

Use of a structured kinetic model of antibody synthesis and secretion for optimization of antibody production systems: II. Transient analysis

The dynamic behavior of the monoclonal antibody (MAb) secretory pathway is studied by transient simulations using our previously developed structured kinetic model for antibody synthesis and secretion by hybridoma cells. The response of the secretory pathway to blocks in specific pathway steps and step changes in characteristic pathway parameters is presented in order to gain a better understanding of pathway dynamics and identify possible rate-limiting steps in the pathway. Model simulations suggest that the step of antibody assembly in the endoplasmic reticulum (ER) is a very good candidate for a rate-limiting step in the antibody secretory pathway in fast-growing hybridoma cells, whereas translation of the heavy and light chains is most likely rate-limiting in slowly growing or stationary phase cells. Transient simulation results are compared with experimentally observed transient changes in specific antibody secretion rates and used to suggest strategies for optimizing antibody secretion in large-scale production systems.

Use of a structured kinetic model of antibody synthesis and secretion for optimization of antibody production systems: I. Steady‐state analysis

Steady-state simulations using our previously developed structured kinetic model of antibody synthesis and secretion by hybridoma cells are used here in conjunction with factorial design analysis to identify intracellular parameters important in determining the specific antibody secretion rate and predict the dependence of this rate on cell specific growth rate. Simulation results suggest that the specific growth rate, the assembly rate of the heavy and light chains and the heavy- and -chain gene dosage can significantly affect the rate of antibody secretion. Based on these results, environmental and/or genetic manipulation approaches are proposed for maximizing the specific antibody secretion rate and the antibody volumetric productivity in large-scale antibody production systems.

A structured model for monoclonal antibody synthesis in exponentially growing and stationary phase hybridoma cells

An initial structured unsegregated kinetic model describing monoclonal antibody synthesis by a murine hybridoma cell line (9.2.27) grown in 1 liter batch cultures is described. The model is based on the intracellular balances of the heavy and light chain coding mRNAs, the intracellular balances of heavy and light chains and the description of the kinetics of heavy and light chain assembly. Model parameters were varied with specific growth rate in order to account for changes in the rates of antibody synthesis and secretion with entrance of the cells from the exponential into the stationary phase of growth. The parameters were varied based. on experimental data obtained in our laboratory on the variation of total cellular RNA content and the half-lives of heavy (H) and light (L) chain mRNAs with specific growth rate, and data from other investigators on immunoglobulin synthesis and secretion. The model successfully predicts the experimentally observed decrease in the intracellular heavy and light chain mRNA levels with entrance of 9.2.27 cells from the exponential into the stationary phase of growth, as well as the extracellular accumulation of antibody (IgG(2a)) during batch culture.

Thermodynamics of information transfer between subunits in oligomeric enzymes and kinetic cooperativity. 1. Thermodynamics of subunit interactions, partition functions and enzyme reaction rate

The strength of quaternary constraints between two subunits of a polymeric enzyme depends upon the number of neighboring subunits and upon whether these subunits are liganded or not. These quaternary constraints between two subunits of a complex polymeric enzyme may be expressed, however, in terms of quaternary constraints that exist within ideal dimers. The influence of quaternary constraints on the reaction rate of a complex polymeric enzyme may thus be expressed in terms of the intersubunit strain that exists within dimers. This conclusion, that was far from evident, appears to be the consequence of the postulates of structural kinetics, and derive as well from usual thermodynamic principles. The structural steady-state equations may be expressed in terms of partition and sub-partition functions. As applied to structural kinetic models, a partition function expresses how, during the steady state, the energy of a population of enzyme molecules is distributed over n states. Similarly a sub-partition function describes how, during the steady state, the energy of these enzyme molecules is partitioned among only n-k of these states. Although the concept of partition function was initially formulated for equilibrium processes, it may be extended without any loss of generality to non-equilibrium processes. Moreover it is reminiscent of the concept of binding polynomial presented some years ago by Wyman for the equilibrium binding of a ligand to a protein. With this formalism derived from statistical mechanics, a structural rate equation may be derived from the ratio of a sub-partition function of degree n-1 and of a partition function of degree n. Again these properties are the consequence of the postulates of structural kinetics associated with simple ideas derived from statistical thermodynamics.

A simple, conceptual mathematical model for the activated sludge process and its variants

A simple structured kinetic model is applied to the activated sludge process. The objective is less to predict exact process performance than to illustrate some of the possibilities and difficulties in producing a comprehensive model for all the process variants. The rate equations are chosen so as to reduce to the Monod equation during balanced growth. Because these rate equations are linear, the cell growth and substrate uptake in a stirred tank can be defined exactly in terms of the average composition of the biomass. It is shown that this is not valid for other forms of rate equations. The stored substrate to protoplasm ratio in the flocs is found to decrease with increasing mean cell residence time. If extracellular biopolymers are included in the stored substrate this corresponds qualitatively to observations of poor flocculation in extended aeration. The model is also applied to the contact stabilization process and is found to be in agreement with the essential process variables.

Structural kinetic model of aromatic polymers

The paper relates to a general structural model for aromatic polymers. It is proposed that phenylene and planar heterocyclic groupings in these polymers are in strictly parallel arrangement (in crystalline regions) relative to one another, and are practically parallel in amorphous regions. The main feature of the systems in question is seen in strong intermolecular interactions restricting torsional oscillations of the groups and hindering their transition to free rotation. The properties and behaviour of aromatic polymers depend to a lesser extent on the rigidity of individual chains and more on that of strongly hindered macromolecular ensembles. The appropriate calculations are carried out aling with an analysis of concrete systems.