Contrasting fates for 6-alpha-methylpenicillin N upon oxidation by deacetoxycephalosporin C synthase (DAOCS) and deacetoxy/deacetylcephalosporin C synthase (DAOC/DACS)

6-alpha -Methylpenicillin N was synthesised via known routes from 6-aminope nicillanic acid, and tested as a substrate for recombinant DAOCS and DAOC/D ACS. Incubation with DAOCS resulted in conversion of 2-oxoglutarate without oxidation of the penicillin substrate ('uncoupled turnover'). Incubation w ith DAOC/DACS resulted in oxidation to the cephem aldehyde. This is the fir st example of substrate-induced 'uncoupled turnover', which has been propos ed to be an editing mechanism for these enzymes. (C) 2001 Elsevier Science Ltd. All rights reserved.