The control of sulphate reduction in Escherichia coli by O-acetyl-l-serine

Abstract

Extracts of E. coli A.T.C.C. 9723 contain serine transacetylase and O-acetylserine sulfhydrase. Synthesis of the latter enzyme is repressed by growth on L-cyst(e)ine and other S compounds. O-Acetyl-L-serine added to cells growing on glutathione or sulfate as source of S induces the enzymes that catalyze the activation of sulfate to adenosine 3[image]-phosphate 5[image]-sulfato-phosphate (EC 2.7.7.4 and 2.7.1.25), the reduction of adenosine 3[image]-phosphate 5[image]-sulfatophosphate to sulfite and the reduction of sulfite to sulfide (EC 1.8.1.2). Hydrogen sulfide is liberated from cultures growing on sulfate as source of S and in the presence of O-acetylserine. The cysE mutants of E. coli K12 lack serine transacetylase. Addition of O-acetylserine permits growth on sulfate as source of S; at the same time the enzymes of sulfate reduction, previously absent, are synthesized. Such mutants have no detectable intracellular cyst(e)ine when starved of S. O-Acetylserine may be necessary for synthesizing the enzymes of sulfate reduction in E. coli. Its action does not appear to be by interference with the repressive control exerted over these enzymes by cyst(e)ine.