A cometabilic kinetics model incorporating enzyme inhbition, inactivation, and recovery: I. Model development, analysis, and testing

Abstract

Cometabolic biodegradation prcesses are important for bioremediation of hazardous waste sites. However, these proceeses are not well understood and have not been modeled thoroughly. Traditional Michaelis-Menten kinetics models often are used, but toxic effects and bacterial responses to toxicity may cause changes in enzyme levels, rendering such models inappropriate. In this article, a conceptual and mathematical model of cometabolic enzyme kinetics i described. Model derivation is based on enzyme/growth-substrate/nongrowth-substrate interaction and incorporates enzyme inhibition (caused by the presence of a cometabolic compound), inactivation (resulting from toxicity of a cometabolic product), and recovery (associated with bacterial synthesis of new enbzyme in response to inactivation). The mathematical model consists of a system of two, nonlinear ordinary differential equations that can be solved implicitly using numerical methods, providing estimates of model parameters. Model analysis shows that growth substraate adn nongrowth substrate oxidation rates are related by a dimensionless constant. Reliability of tehy model solution prcedure is verifiedl by abnalyzing data ses, containing random error, from simulated experimentss with trichhloroethyylene (TCE) degradation by ammonia-oxidizing bacterialunder various conditions. Estimation of the recovery rate contant is deterimined to be sensitive to intial TCE concentration. Model assumptions are evaluated in a companion article using data from TCE degradation experiments with amoniaoxidizing bacteria. (c) 1995 John Wiley & Sons, Inc.

Laboratory evaluation of a two-stage treatment system for TCE cometabolism by a methane-oxidizing mixed culture

“…Clearly, a simple competitive inhibition model would not be able to simulate the rate and extent of TCE cometabolism observed for these cultures. Several recently proposed models do include the effects of growth, product toxicity, reducing power depletion and regeneration, and enzyme inhibition (Chang and Alvarez-Cohen, 1995a;Ely et al, 1995). However, a source of reducing power such as formate that is inhibitory under some conditions has not been reported until now or included in models.…”

NAD(P)H:Flavin Mononucleotide Oxidoreductase Inactivation during 2,4,6-Trinitrotoluene Reduction

“…At a molecular level, enzyme-substrate interactions control the rate of transformation through processes including enzyme limitation, substrate inhibition, cofactor limitation, enzyme inactivation, and enzyme recovery (18). Frequently, these processes are described on the cellular level by the more generic terms of toxicity and cometabolic yield (2).…”

“…For example, in an investigation of TNT reduction by a mixed culture undergoing fermentation, only when intracellular kinetics were considered did the model adequately predict TNT reduction (12). The benefit of enzyme level models of cometabolism has already been explored in the area of trichloroethene biodegradation, where the availability of intracellular electrons plays a key role (18,19,52,62,65). This work represents the first step in developing a comprehensive enzyme level understanding of nitroarene biotransformation.…”

“…A greater understanding of the fundamental mechanisms that control TNT transformation is required to predict the aggregate transformation of TNT in the environment. Processes at the enzyme level such as enzyme inhibition, enzyme inactivation, and enzyme recovery ultimately control cometabolic reaction kinetics (18). To initiate the development of a biochemically and kinetically valid model for TNT reduction by bacterial cells, a reductionist model system was employed consisting of a single enzyme, NAD(P)H:flavin mononucleotide (FMN) oxidoreductase derived from Photobacterium fischeri, known to exhibit nitroarene reduction activity (63).…”

Kinetics of Hydrolyzing Isolated Soy Protein by an Endopeptidase and its Conceptual Application in Process Engineering

“…Due to these complexities, it is difficult to describe such a hydrolysis process using a simple kinetics model (Markovic et al, 1988). Several authors have proposed kinetics models for actual hydrolysis systems (Gonzalez-Tello et al, 1994;O'Meara & Munro, 1985;Ely, Williamson, Guenther, Hyman, & Arp, 1995;Barros & Malcata, 2002). These models are based on different assumptions and show good fit to experimental data.…”