Biological breakdown of benzylpenicillin by preformed mats of penicillin-producing organisms.

1. Penicillium chrysogenum and Aspergillus flavus degraded benzylpenicillin in the same way. 2. Degradation of the antibiotic was initiated by the cleavage of phenylacetic acid from 6-aminopenicillanic acid. 3. Phenylacetic acid was left unchanged whereas 6-aminopenicillanic acid was degraded into cysteine and valine. This reaction is probably complex. 4. Cysteine was not utilized but valine was cleaved into acetone and glycine. Catabolism of valine by the preformed mats of the two moulds confirms this result. This step probably involves the formation of propan-2-ol. 5. Cleavage of benzylpenicillin into phenylacetic acid and 6-aminopenicillanic acid was performed through the activity of a cellular-bound enzyme.