Clavulanic acid biosynthesis; the final steps

The chemically unstable anabolite (3R,5R)-clavulanate-9-aldehyde 1 and an N ADPH dependent dehydrogenase have been detected in the broth of Streptomyce s clavuligerus. The purified enzyme was shown to make clavulanic acid by re duction of the aldehydic moiety of synthetic 1 to the allylic alcohol of cl avulanic acid 2. A DNA sequence corresponding to the enzyme's N-terminal am ino acid sequence was located within the clavulanic acid biosynthetic gene cluster. We have named this novel enzyme clavulanic acid dehydrogenase (CAD ). In an attempt to determine the origin of 1, fermentations of S. clavulig erus were fed ornithine labelled with stable isotopes in the carboxy group. The results of these experiments are discussed.