TpnL-mediated conversion of thiostrepton A (1) to thiostrepton Aa (7). (A) HPLC analyses of culture extracts from (a) S.laurentii, (b) S. laurentii HI0, (c) S. laurentii HI1, (d) coinjection of S. laurentii and HI1 extracts, and (e) coinjection of S. laurentii HI0 and HI1 extracts. (B) HPLC analyses of TpnL activity. Reactions omitting TpnL are shown at the top and reactions including TpnL are shown at the bottom. Reaction mixtures were incubated for (i) 0 min, (ii) 10 min, (iii) 60 min, and (iv) 6 h. Absorbance was monitored at 254 nm. 1 is represented by ○ and 7 by ●.