O.Z. developed AcmB mutant variants, expressed and purified the enzymes, M.F. conducted stopped-flow steady-state Ping Pong kinetics, analysed results K.K. refined the structure of AcmB, co-authored the manuscript (crystallographic sections) M.O. provided assistance in pre-steady state kinetics, edited the manuscript A.B. supervised P.W., provided funding, edited the manuscript E.N. developed conditions for enzyme crystallization, edited the manuscript W.M. oversaw initial experiments and edited the manuscript A.M.W. purified the enzyme, conducted the bioinformatic analysis, co-authored the bioinformatic analysis section, created figures M.S. designed the study, provided funding, supervised M.G, P.W., M.P., O.Z., M. F., analysed and curated all data, co-authored and edited the manuscript,