THE CONTROL OF SULPHATE REDUCTION IN BACTERIA

Abstract

An enzyme from Escherichia coli 9723 that reduces adenosine 3[image]-phosphate 5[image]-sulfatophosphate to inorganic sulfite is described. Extracts of E. coli K12 and Bacillus subtilis 13 79 contain a similar enzyme. This reductase and sulfite reductase (EC 1.8.1.2) of E. coli 9723, E. coli K12 and B. subtilis are repressed by growth in the presence of L-cystine. Cysteine synthase (EC 4.2.1.22) is unaffected. Growth of E. coli 9723 on inorganic sulfite represses the sulfate-activating enzymes (EC 2.7.7.4 and 2.7.1.25) almost completely but has little effect on sulfite reductase. Growth on 0.042[long dash]0.056m[image]-L-cystine gives a similar result. Such differential repression by cyst (e)ine prevents E. coli, when growing on sulfite, from synthesizing unnecessary enzymes.