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 H(2)O(2) to O(2) and H(2)O. However, catalases evolved when metabolism was largely sulfur-based, long before O(2) and reactive oxygen species (ROS) became abundant, suggesting catalase metabolizes reactive sulfide species (RSS). Here we examine catalase metabolism of H(2)S(n), the sulfur analog of H(2)O(2), hydrogen sulfide (H(2)S) and other sulfur-bearing molecules using H(2)S-specific amperometric electrodes and fluorophores to measure polysulfides (H(2)S(n); SSP4) and ROS (dichlorofluorescein, DCF). Catalase eliminated H(2)S(n), but did not anaerobically generate H(2)S, the expected product of dismutation. Instead, catalase concentration- and oxygen-dependently metabolized H(2)S and in so doing acted as a sulfide oxidase with a P(50) of 20 mmHg. H(2)O(2) had little effect on catalase-mediated H(2)S metabolism but in the presence of the catalase inhibitor, sodium azide (Az), H(2)O(2) rapidly and efficiently expedited H(2)S metabolism in both normoxia and hypoxia suggesting H(2)O(2) is an effective electron acceptor in this reaction. Unexpectedly, catalase concentration-dependently generated H(2)S from dithiothreitol (DTT) in both normoxia and hypoxia, concomitantly oxidizing H(2)S in the presence of O(2). H(2)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 H(2)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.