Molecular Structure
From a chemical standpoint, this substance is a classic tripeptide. This means the core of the molecule consists of a chain of exactly three amino acid residues linked together.
The molecule includes the following components:
- $\gamma$-glutamate;
- cysteine;
- glycine.
Notably, the molecule is neither a dipeptide, tetrapeptide, nor pentapeptide. This strict three-component structure (tripeptide) provides the necessary spatial and chemical properties to participate in oxidation-reduction processes within living cells.
Reduced and Oxidized Forms
In biological systems, this compound continuously transitions between two functional states:
- Reduced form ($\Gamma-SH$). In this state, the molecule contains a free sulfhydryl group ($-SH$). This chemically active group acts as an electron donor when neutralizing dangerous compounds.
- Oxidized form ($\Gamma-S-S-\Gamma$). This forms after the molecule donates its reducing equivalents. In this state, two molecules bind together via a strong disulfide bond ($-S-S-$).
Peroxide Neutralization Cycle
The neutralization of hazardous compounds is organized as a cycle comprising two coupled reactions. These are not independent processes, but a strictly sequential chain of transformations where the product of one reaction serves as the substrate for the next.
The first stage is the direct neutralization of hydrogen peroxide ($H_2O_2$), catalyzed by the enzyme glutathione peroxidase.
The reaction equation is: $$2\Gamma-SH + H_2O_2 \rightarrow \Gamma-S-S-\Gamma + 2H_2O$$
During this coupled process, two molecules of reduced glutathione are oxidized, while toxic hydrogen peroxide is converted into harmless water molecules.
Regeneration Process
To sustain antioxidant defense, the oxidized form of the molecule must be returned to its original, functionally active state. This is the second stage of the coupled cycle.
Reduction is mediated by the enzyme glutathione reductase. This reaction requires an energy source and reducing equivalents—specifically $NADPH$ and hydrogen ions ($H^+$).
The chemical essence of the process: $$\Gamma-S-S-\Gamma + NADPH + H^+ \rightarrow 2\Gamma-SH + NADP^+$$
As a result, the disulfide bond is cleaved, and the cell regains two molecules with active sulfhydryl groups, ready for a new peroxide neutralization cycle.