Activation of alternative oxidase and uncoupling protein lowers hydrogen peroxide formation in amoeba Acanthamoeba castellanii mitochondria

Mitochondria of amoeba Acanthamoeba castellanii were used to determine the role of two energy‐dissipating systems, i.e., a free fatty acid (FFA)‐activated, purine nucleotide‐inhibited uncoupling protein (AcUCP) and a FFA‐insensitive, purine nucleotide‐activated ubiquinol alternative oxidase (AcAOX), in decreasing reactive oxygen species production in unicellular organisms. It is shown that the activation of AcUCP by externally added FFA resulted in a strong decrease in H 2 O 2 production, whilst the inhibition of the FFA acid‐induced AcUCP activity by GDP or addition of bovine serum albumin (BSA) enhanced production of H 2 O 2 . Similarly, the activation of antimycin‐resistant AcAOX‐mediated respiration by GMP significantly lowered H 2 O 2 production, while inhibition of the oxidase by benzohydroxamate cancelled the GMP‐induced effect on H 2 O 2 production. When active together, both energy‐dissipating systems revealed a cumulative effect on decreasing H 2 O 2 formation. The results suggest that protection against mitochondrial oxidative stress may be a physiological role of AOX and UCP in unicellulars, such as A. castellanii .