Simulation modeling of glutamate cysteine ligase activity

L-Y-glutamyl-L-cysteinyl glycine, or glutathione, as one of the basic intracellular antioxidants, plays a vital role in cellular metabolism. In mammalian cells, glutathione is synthesized via two steps. The first step that is considered rate limiting is catalyzed by glutamate cysteine ligase. In this work, a stochastic algorithm based on continuous-time Markov chains was used to simulate the activity of glutamate-cysteine ligase. Several different mechanisms of enzymatic activity including reversible inhibition of glutathione, and an ATP binding motif have been considered. Based on physiological metabolite measurements made for human erythrocytes, the activity of glutamate cysteine ligase was determined. There are many possible ways for substrates to bind to an active site of the studied enzyme, but, only the mechanism by which primary binding to ATP can occur makes it possible to obtain the catalytic rate value similar to that of the experimentally measured glutamatecysteine ligase activity relative to physiological concentrations of substrates. In other cases, the values differ by more than one order of magnitude. The performed analysis allows the conclusion that when models for glutathione biosynthesis are constructed in vivo conditions, the ATP concentration and reversible inhibition of glutathione should be taken into account.

glutathione, Glutamate-cysteine ligase, simulation modeling, stochastic algorithm