Interaction of Cu,Zn Superoxide Dismutase with Hydrogen Sulfide

• Published in: Archives of biochemistry and biophysics 1995-04, Vol.318 (2), p.251-263
• Main Authors: Searcy, D.G., Whitehead, J.P., Maroney, M.J.
• Format: Article
• Language: English
• Subjects: Animals; Cattle; Cytochrome c Group - analysis; Electron Spin Resonance Spectroscopy; Erythrocytes - enzymology; Hydrogen Sulfide - metabolism; Kinetics; Models, Theoretical; Saccharomyces cerevisiae - enzymology; Spectrophotometry; Superoxide Dismutase - blood; Superoxide Dismutase - chemistry; Superoxide Dismutase - metabolism
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.1995.1228

Addition of HS − enhanced the O − 2scavenging activity of bovine erythrocyte Cu,Zn superoxide dismutase (EC 1.15.1.1) by about twofold. The positive effect was measured using a diverse selection of SOD activity assays, and cannot be an artifact restricted to any single technique. K m values for HS − varied in different assay techniques, but we estimate K m ≍ 80 μM HS −. In contrast to HS −, other small molecules tested with SOD either had little effect or were inhibitory. Consumption of HS − and O − 2 occurred in nearly 1:1 mole ratio. The products were H 2O 2 and sulfane sulfur, such as either elemental sulfur or polysulfide. Binding of HS − to the enzyme was rapid, with k > 10 7 M −1 s −1. The resulting complex exhibited a Cu-to-S charge-transfer absorbance band at 345 nm and an altered Cu(II) EPR spectrum. Taken together, these observations suggest that HS − binds at the catalytic Cu center of SOD and can be a genuine substrate of the enzyme.