Cysteine biosynthesis in Salmonella typhimurium: the presence of ATP-sulfurylase and APS-kinase in various cysteine-requiring mutants.

Enzymatic tests were performed on a series of cysteine-requiring mutants for the presence of the sulfate activating enzymes. ATP-sulfurylase (sulfate adenylyltransferase EC 2.7.7.4) and APS-kinase (adenylylsulfate kinase EC 2.7.1.25). The enzymatic products adenosine 5'-[35S]sulfatophosphate and adenosine 3'-phosphate 5'-[35S]sulfatophosphate were identified by paper electrophoresis and measured quantitatively without elution from the paper. Cys mutants mapping in cistrons, A, H, I, J, G, and Ea contain both enzymes. Mutation in the D cistron leads to the loss of ATP-sulfurylase. Mutants mapping in the C cistron lack APS-kinase. Ba, Bb, and Bc mutants lack both enzymes. The control of the synthesis of these enzymes by cysteine was examined. Both enzymes are missing when cells are grown on cysteine.