A redox cycling mechanism of action for 2,3-dichloro-1,4-naphthoquinone with mitochondrial membranes and the role of sulfhydryl groups

The addition of 2,3-dichloro-l,4-naphthoquinone (CNQ) to substrate-depleted, GSH-supplemented rat liver mitochondria resulted in a dose-dependent depletion of readable suflhydryl groups and a concomitant increase in mitochondrial disulfide content at a ratio of 2 thiols depleted/disulfide generated. The molar ratio of thiol depleted/CNQ added approached 20 at low CNQ concentrations and was unity at higher doses. The addition of CNQ to substrate-depleted mitochondrial suspensions resulted in O₂; consumption which increased with increasing concentrations of mitochondria and was sensitive to N-ethylmaleimide (NEM) which establishes the ability of CNQ to interact with mitochondrial thiol redox centers. The CNQ-mediated large amplitude swelling of rat liver mitochondria was exacerbated by thiol oxidizing agents and depressed by disulfide reducing agents. A redox cycling mechanism between mitochondrial thiol groups, CNQ and oxygen was proposed to lower the matrix glutathione pool and make the mitochondria more susceptable to toxic oxygen radicals which induce swelling in isolated mitochondrial suspensions. In support of this mechanism, α-tocopherol was shown to prevent the CNQ-mediated swelling process. Beef heart mitochondrial NADH was oxidized by CNQ in a $\text{1}\text{1}$ molar ratio anaerobically and in a $\text{3}\text{1}$ molar ratio under aerobic conditions, whereas the fully reduced quinone, CNQH₂, oxidized NADH aerobically but not anaerobically. Thus, CNQ is capable of interacting with NADH of the mitochondrial electron transport chain in a redox cycling fashion.