Mitochondrial production of superoxide and hydrogen peroxide is potentially important in
cell signaling and disease. Eleven distinct mitochondrial sites that differ markedly in capacity
are known to leak electrons to oxygen to produce O 2 ̇̄ and/or H 2 O 2. We discuss their
contributions to O 2 ̇̄/H 2 O 2 production under native conditions in mitochondria oxidizing
different substrates and in conditions mimicking physical exercise and the changes in their
capacities after caloric restriction. We review the use of S1QELs and S3QELs, suppressors …