That the inhibition could be reversed by L - α - aminoadipic acid led to the postulations [10] that (i) L - α - aminoadipic acid was involved in penicillin biosynthesis although it did not end up in the fi nal penicillin molecule, (ii) penicillin was derived from α - ketoglutarate and acetyl - CoA via the fungal lysine biosynthetic pathway, and (iii) lysine inhibition of penicillin biosynthesis was due to feedback inhibition by lysine of its own biosynthetic pathway, thus limiting L - α - aminoadipic acid formation. Independently, Arnstein and colleagues [11] detected the tripeptide δ - ( α - aminoadipyl) - cysteinylvaline ( ACV )
as an intracellular compound in P. chrysogenum .