The metabolism of toxicants is generally divided into three phases:
- Phase I Reactions: These involve the introduction or exposure of functional groups via oxidation, reduction, or hydrolysis. Cytochrome P450 enzymes play a significant role in Phase I reactions, which can sometimes convert a non-toxic substance into a toxic metabolite.
- Phase II Reactions: These involve conjugation reactions where the toxicant or its Phase I metabolites are linked to an endogenous molecule like glucuronic acid, sulfate, or glutathione. These reactions generally increase the water solubility of the toxicant, facilitating its excretion.
- Phase III Reactions: These involve further modifications and transport processes that prepare the toxicant for excretion from the cell. Transport proteins like P-glycoprotein play critical roles in this phase.
