S-Adenosylmethionine as a common biochemical substrate for the rapid and chronic growth stages of M. tuberculosis . The pathways of S-adenosylmethionine usage and the potential recycling routes of methionine and ATP are shown. The enzymes which catalyse the reactions are: 1 methionine adenosyltransferase, 2 S-adenosylmethionine decarboxylase, 3 spermidine/spermine aminopropyltransferase, 4 methylthioadenosine phosphorylase, 4a methylthioadenosine nucleosidase, 4b methylthioribose kinase, 5 four steps not shown, 6 aminotransferase, 7 mycolic acid methyltransferases, 8 S-adenosylhomocysteine hydrolase, 8a S-adenosylhomocysteine nucleosidase, 8b S-ribosylhomocysteine hydrolase, and 9 methionine synthetase. It has not yet been determined in M. tuberculosis whether enzyme 4 or 4a/4b, and 8 or 8a/8b catalyses the recycling of methionine. The exact aminotransferase catalysing step 6 has also not been elucidated.