The utilization of l-cystinyl-l-valine for penicillin biosynthesis

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Abstract
The incorporation of radioactivity from L-cystinyl-L-fcarboxy-l^C] valine, L-cystinyl-D-[carboxy-14C] valine and uniformly labelled L-[14c]-valine into penicillin by washed mycelium of Penicillium chrysogenum WIS 51-20 F 3 has been compared with their utilization for protein synthesis. L-Cystinyl-D-[carboxy-14C]valine was not metabolized to any significant extent. L-Cystinyl-L-[carboxy-14C]valine was used preferentially for penicillin biosynthesis, indicating that this peptide can be utilized without hydrolysis into cystine and valine. The extent of this direct utilization of L-cystinyl-L-valine for penicillin formation appears to be quantitatively limited and the existence of a pathway of penicillin biosynthesis from cystine and valine, which does not involve cystinyl- or cysteinyl-valine as obligatory intermediates, is suggested.