title: A study on the reaction mechanism of adenosine 5'-phosphosulfate reductase from Thiobacillus thioparus, an iron-sulfur flavoprotein.
abstract: The reaction mechanism of adenosine 5'-phosphosulfate (APS) reductase (EC 1.8.99.2) from Thiobacillus thioparus was studied using difference spectrum and stopped-flow techniques. The enzyme-bound FAD was rapidly reduced by sulfite with a first order rate constant of 97.1 s-1. The addition of AMP induced further spectral changes in the reduced enzyme which were consistent with the oxidation of FADH2 to the red (anionic) semiquinone FADH-) and the concomitant reduction of nonheme iron to the ferrous state. Superoxide dismutase (EC 1.15.1.1) or anaerobiosis inhibited the reduction of cytochrome c by the enzyme only to the extent of 25-35%, indicating the existence of a direct reduction of cytochrome c by the enzyme without involving O2-. the activity of enzyme with cytochrome c was inhibited by increasing the potassium phosphate concentration, the inhibition being more pronounced with horse heart cytochrome c than with Candida krusei cytochrome c.
mesh_terms: D000249:Adenosine Monophosphate / Q000031:analogs & derivatives; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D007700:Kinetics; D010088:Oxidoreductases / Q000378:metabolism*; D010710:Phosphates; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D013447:Sulfites; D013464:Sulfuric Acids; D013855:Thiobacillus / Q000201:enzymology*
chemical_list: D007506:Iron-Sulfur Proteins; D010710:Phosphates; D013447:Sulfites; D013464:Sulfuric Acids; D000249:Adenosine Monophosphate; D010088:Oxidoreductases