Inhibition of penicillin biosynthesis by δ-(L-α-amino-δ-adipyl)-L-cysteinylglycine. Evidence for initial β-lactam ring formation

Abstract
Incubation of the modified substrate, δ-(L-α-amino-δ-adipyl)-L-cysteinylglycine (ACG) with the enzyme isopenicillin N synthetase resulted in inhibition at a rate which paralleled the rate of release of tritium (as 3HOH) from the [3-3H]cysteinyl isotopomer of ACG, while incubation of the [U-14C]cysteinyl isotopomer of ACG with the enzyme, in the presence of NaB3H4, gave rise to 3H-labelled ACG, in which the tritium was shown to reside at the 3-cysteinyl position; these results are in accord with β-lactam formation during enzymic transformation of this substrate.

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