Antivitamin B6 activity of L-penicillamine in Escherichia coli

Escherichia coli wild strain K12 and the vitamin B6 requiring mutant strain KG980 were compared with respect to the growth inhibition by L-penicillamine and the reversal of inhibition with pyridoxine. The growth of KG980 was much more severely inhibited than that of K12 by relatively low concentrations of L-penicillamine, when KG980 was grown with a usually sufficient concentration of pyridoxine. The following findings indicated that this was because L-penicillamine caused vitamin B6 deficiency in KG980; (a) addition of excess pyridoxine significantly reversed the inhibition, (b) comparison of the growth with various concentrations of pyridoxine showed that the vitamin requirement became higher upon addition of L-penicillamine. Examination of cellular vitamin B6 compounds showed that pyridoxal 5'-phosphate was markedly decreased when L-penicillamine was present, in agreement with the probable reaction of the inhibitor with the coenzyme. On the other hand, the growth inhibition of K12 appeared independent of vitamin B6 deficiency, and the cellular pyridoxal 5,-phosphate was found not to be markedly reduced by the presence of L-penicillamine, while the total of vitamin B6 compounds, probably including the product formed by the coenzyme and the inhibitor, increased clearly. The results, therefore, suggest that the wild strain of E. coli can avoid the deficiency of vitamin B6 by enhancing its biosynthesis, although L-penicillamine acts as an antivitamin B6.