This study examined the antioxidant mechanisms of glutathione, L-cysteine, and methionine in preventing oxidative DNA damage caused by the Fenton reaction of iron and copper. Cyclic voltammetry studies showed that while the antioxidants bound to the metals, they did not shift the redox potential enough to prevent the Fenton reaction. Additionally, the antioxidants were not electrochemically active, indicating they were not acting as reactive oxygen species scavengers. Therefore, the primary mechanism of antioxidant activity for these molecules is metal coordination, not ROS scavenging.