Purification of clostridial mature AdhE and the butanol dehydrogenase domain from the heterologous host E. coli. Separation was performed with an SDS-6 to 25% (wt/vol) polyacrylamide linear gradient gel and was followed by silver staining. Lane 1, marker proteins; lanes 2 and 8, crude extract from WL3(pGP1-2, pTWa4-2) (negative control); lanes 3 and 7, crude extract from WL3(pGP1-2, pTWa4-2::adhE6×His); lanes 4 and 6, fractions after affinity chromatography with Ni-NTA; lane 5, fraction after affinity chromatography with Reactive Green 19.