Cyclization of phenylacetyl-L-cysteinyl-D-valine to benzylpenicillin using cell-free extracts of Streptomyces clavuligerus.

Benzylpenicillin, a typical antibiotic produced by some species of fungi, was obtained by direct cyclization of the heteropeptide phenylacetyl-L-cysteinyl-D-valine using cell-free extracts of Streptomyces clavuligerus. This is the first description of evidence of the synthesis of benzylpenicillin from a non natural molecule using a bacterial enzyme.