Catalase as a sulfide-sulfur oxido-reductase: An ancient (and modern?) regulator of reactive sulfur species (RSS).

Catalase is well-known as an antioxidant dismutating H2 O2 to O2 and H2 O. However, catalases evolved when metabolism was largely sulfur-based, long before O2 and reactive oxygen species (ROS) became abundant, suggesting catalase metabolizes reactive sulfide species (RSS). Here we examine catalase metabolism of H2 Sn , the sulfur analog of H2 O2 , hydrogen sulfide (H2 S) and other sulfur-bearing molecules using H2 S-specific amperometric electrodes and fluorophores to measure polysulfides (H2 Sn ; SSP4) and ROS (dichlorofluorescein, DCF). Catalase eliminated H2 Sn , but did not anaerobically generate H2 S, the expected product of dismutation. Instead, catalase concentration- and oxygen-dependently metabolized H2 S and in so doing acted as a sulfide oxidase with a P50 of 20mmHg. H2 O2 had little effect on catalase-mediated H2 S metabolism but in the presence of the catalase inhibitor, sodium azide (Az), H2 O2 rapidly and efficiently expedited H2 S metabolism in both normoxia and hypoxia suggesting H2 O2 is an effective electron acceptor in this reaction. Unexpectedly, catalase concentration-dependently generated H2 S from dithiothreitol (DTT) in both normoxia and hypoxia, concomitantly oxidizing H2 S in the presence of O2 . H2 S production from DTT was inhibited by carbon monoxide and augmented by NADPH suggesting that catalase heme-iron is the catalytic site and that NADPH provides reducing equivalents. Catalase also generated H2 S from garlic oil, diallyltrisulfide, thioredoxin and sulfur dioxide, but not from sulfite, metabisulfite, carbonyl sulfide, cysteine, cystine, glutathione or oxidized glutathione. Oxidase activity was also present in catalase from Aspergillus niger. These results show that catalase can act as either a sulfide oxidase or sulfur reductase and they suggest that these activities likely played a prominent role in sulfur metabolism during evolution and may continue do so in modern cells as well. This also appears to be the first observation of catalase reductase activity independent of peroxide dismutation.