Inhibition of penicillin formation by amino acid analogs

Using resting mycelial suspensions, it was found that S-ethyl-dl-cysteine and α-methyl-dl-valine inhibit penicillin synthesis from lactose. Reversal by l-cystine and l-valine, respectively, was observed. Whereas l-valine can be used for penicillin synthesis, the d-form is an inhibitor. Conclusions based on previous tracer studies were confirmed.