Figure 2.

(A) MALDI-TOF mass spectra of (i) unmodified His₆–CaoA. [M + H]⁺ exp. m/z = 7025; obsd m/z = 7022. (ii) His₆–CaoA modified by CaoK in E. coli. [M + H]⁺ exp. = 7025, obsd = 7028; (M + H + HPO₃)⁺ exp. = 7105, obsd = 7109; (M + H + 2HPO₃)⁺ exp. = 7185, obsd = 7188; (M + H + 3HPO₃)⁺ exp. = 7265, obsd = 7271; (M + H + 4HPO₃)⁺ exp. = 7345, obsd = 7349. (iii) His₆–CaoA modified by CaoK and CaoY in E. coli. (M + H – 8H₂O)⁺ exp. = 6881, obsd = 6883; (M + H – 8H₂O + GSH)⁺ exp. = 7186, obsd = 7190. (iv) His₆–CaoA modified by His₆–CaoK–CaoY dehydratase complex in vitro with adenosine triphosphate (ATP) and MgCl₂. (M + H – 8H₂O)⁺ exp. = 6881, obsd = 6878. (B, C) Liquid chromatography coupled with electrospray ionization-quadrupole-time of flight (LC-ESI-QTOF) mass spectrum of (B) Glu-C digested His₆–CaoA core peptide modified by CaoK–CaoY during co-expression in E. coli ([M + 2H]²⁺ exp. = 1038.4588; obsd = 1038.4594), and (C) MS–MS fragmentation pattern of Glu-C digested His₆–CaoA core peptide modified by CaoK–CaoY in E. coli. For fragment masses, see Table S3.