A mechanistic mathematical model for the catalytic action ofglutathione peroxidase

Abstract

Glutathione peroxidase (GPx) is a well-known seleno-enzyme that protects cells from oxidative stress (e.g., lipid peroxidation and oxidation of other cellular proteins and macromolecules), by catalyzing the reduction of harmful peroxides (e.g., hydrogen peroxide: H2O2) with reduced glutathione (GSH). However, the catalytic mechanism of GPx kinetics is not well characterized in terms of a mathematical model. We developed here a mechanistic mathematical model of GPx kinetics by considering a unified catalytic scheme and estimated the unknown model parameters based on different experimental data from the literature on the kinetics of the enzyme. The model predictions are consistent with the consensus that GPx operates via a ping-pong mechanism. The unified catalytic scheme proposed here for GPx kinetics clarifies various anomalies, such as what are the individual steps in the catalytic scheme by estimating their associated rate constant values and a plausible rationale for the contradicting experimental results. The developed model presents a unique opportunity to understand the effects of pH and product GSSG on the GPx activity under both physiological and pathophysiological conditions. Although model parameters related to the product GSSG were not identifiable due to lack of product-inhibition data, the preliminary model simulations with the assumed range of parameters show that the inhibition by the product GSSG is negligible, consistent with what is known in the literature. In addition, the model is able to simulate the bi-modal behavior of the GPx activity with respect to pH with the pH-range for maximal GPx activity decreasing significantly as the GSH levels decrease and H2O2 provides a key component for an integrated model of H2O2 levels increase (characteristics of oxidative stress). The model balance under normal and oxidative stress conditions.

Mechanistic characterization of the thioredoxin system in the removal of hydrogen peroxide

“…The major pathways responsible for H 2 O 2 detoxification in various cell types include the GSH and Trx systems. Mechanistic mathematical models have been recently developed for the GSH system that provides novel quantitative insights into the catalytic mechanisms of GR and GPx enzymes [50, 51] in the removal of H 2 O 2 . However, the same level of mechanistic characterization of the Trx system is not available despite several experimental studies performed on the system (Prx and TrxR enzymes).…”

“…Similarly, for Prx we assumed the single protonated activated forms of the enzyme at each step where water is released as the reaction product, namely at intermediate enzyme state E 2 and E 3 . A similar approach was considered in our previous study [51] to identify the pH-mediated kinetic behavior of the mechanistically identical GPx enzyme. The model analyses of the peroxidase enzymes show that the activities of these enzymes are considerably reduced to detoxify H 2 O 2 in the event of acidic pH, leading to higher [H 2 O 2 ] which is the hallmark of oxidative stress.…”

A Biophysical Systems Approach to Identifying the Pathways of Acute and Chronic Doxorubicin Mitochondrial Cardiotoxicity

“…Computational models have already been used to study mitochondrial dysfunction [22], ROS generation [23, 24] and ROS scavenging [25, 26]. However, this is the first time, that this kind of models has been used to study drug cardiotoxicity.…”

Modeling the detailed kinetics of mitochondrial cytochromecoxidase: Catalytic mechanism and nitric oxide inhibition

“…The model also shows CcO resides mainly in the O 2 -bound form under deenergized mitochondrial conditions, which is altered as mitochondria become more polarized leading to accumulation of other intermediate enzyme states, depending on NO concentration ([NO]). Therefore, the developed CcO model is mechanistic and thermodynamically constrained and suitable to be incorporated into other components of existing mitochondrial bioenergetics models (5,35,36,38) to understand the role of the enzyme in controlling OxPhos in health and disease states, for example, ischemia-reperfusion injury.…”