title: Stable isotope fractionation by Clostridium pasteurianum. 2. Regulation of sulfite reductases by sulfur amino acids and their influence on sulfur isotope fractionation during SO32- and SO42- reduction.
abstract: In addition to an assimilatory sulfite reductase, studies of cultures of Clostridium pasteurianum supplemented with methionine, cysteine, and 35SO42- provides evidence for another reductase which is induced by SO32-. This inducible reductase appears to be dissimaltory because of the copious sulfide production arising when the cells are grown on SO32-. Cysteine can repress the assimilatory sulfite reductase but does not affect the inducible reductase. During late logarithmic growth on 1 mM SO42- + 10mM cysteine, depression of the inducible reductase occurred along with increased sulfide production. The presence of 1 mM cysteine and (or) 1 mM cysteine and (or) 1 mM methionine does not affect the inverse sulfur isotope effect for evolved H2S. However, 5 and 10 mM cysteine reduce the maximum delta34S value for released H2S from +40 to 10%. A small conversion of cysteine to H2S by C. pasteurianum occurs, but only in the stationary phase.
mesh_terms: D002474:Cell-Free System; D005591:Chemical Fractionation; D003013:Clostridium / Q000378:metabolism*; D003545:Cysteine / Q000494:pharmacology*; D004794:Enzyme Repression; D006862:Hydrogen Sulfide / Q000378:metabolism; D008715:Methionine / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000096:biosynthesis* / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*; D013447:Sulfites / Q000378:metabolism*; D013462:Sulfur Radioisotopes
chemical_list: D013431:Sulfates; D013447:Sulfites; D013462:Sulfur Radioisotopes; D008715:Methionine; D010088:Oxidoreductases; D003545:Cysteine; D006862:Hydrogen Sulfide