Theaflavins inhibit the ATP synthase and the respiratory chain without increasing superoxide production

Four dietary polyphenols, theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate and theaflavin-3,3′-digallate (TF3), have been isolated from black tea, and their effects on oxidative phosphorylation and superoxide production in a model system (Escherichia coli) have been examined. The esterified theaflavins were all potent inhibitors of the membrane-bound adenosine triphosphate (ATP) synthase, inhibiting at least 90% of the activity, with IC50 values in the range of 10–20 μM. ATP-driven proton translocation was inhibited in a similar fashion, as was the purified F1-ATPase, indicating that the primary site of inhibition was in the F1 sector. Computer modeling studies supported this interpretation. All four theaflavins were also inhibitory towards the electron transport chain, whether through complex I (NDH-1) or the alternative NADH dehydrogenase (NDH-2). Inhibition of NDH-1 by TF3 appeared to be competitive with respect to NADH, and this was supported by computer modeling studies. Rates of superoxide production during NADH oxidation by each dehydrogenase were measured. Superoxide production was completely eliminated in the presence of about 15 μM TF3, suggesting that inhibition of the respiratory chain by theaflavins does not contribute to superoxide production.