A catalase–peroxidase for oxidation of β-lactams to their (R)-sulfoxides

In this communication we report for the first time a biocatalytic method for stereoselective oxidation of β-lactams, represented by penicillin-G, penicillin-V and cephalosporin-G to their (R)-sulfoxides. The method involves use of a bacterium, identified as Bacillus pumilis as biocatalyst. The enzyme responsible for oxidase activity has been purified and characterized as catalase–peroxidase (KatG). KatG of B. pumilis is a heme containing protein showing characteristic heme spectra with soret peak at 406 nm and visible peaks at 503 and 635 nm. The major properties that distinguish B. pumilis KatG from other bacterial KatGs are (i) it is a monomer and contains one heme per monomer, whereas KatGs of other bacteria are dimers or tetramers and have low heme content of about one per dimer or two per tetramer and (ii) its 12-residue, N-terminal sequence obtained by Edman degradation did not show significant similarity with any of known KatGs.

► We have described a new catalase–peroxidase (KatG) from Bacillus pumilis.
► KatG of B. pumilis stereoselectively oxidized β-lactams to their (R)-sulfoxides.
► Diastereomeric excess of (R)-sulfoxides was 100%.
► No over-oxidation to sulfones was detected.
► KatG of B. pumilis was characterized as 62 kDa, monomeric heme containing protein.