L-Lactate generates hydrogen peroxide in purified rat liver mitochondria due to the putative L-lactate oxidase localized in the intermembrane space

In order to ascertain whether and how mitochondria can produce hydrogen peroxide (H(2)O(2)) as a result of L-lactate addition, we monitored H(2)O(2) generation in rat liver mitochondria and in submitochondrial fractions free of peroxisomal and cytosolic contamination. We found that H(2)O(2) is produced independently on the respiratory chain with 1:1 stoichiometry with pyruvate, due to a putative flavine-dependent L-lactate oxidase restricted to the intermembrane space. The L-lactate oxidase reaction shows a hyperbolic dependence on L-lactate concentration and is inhibited by NAD(+) in a competitive manner, being the enzyme different from the L-lactate dehydrogenase isoenzymes as shown by their pH profiles. (C) 2010 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.