Oxygen utilisation by isopenicillin N synthase from Penicillium chrysogenum.

The enzyme isopenicillin N synthase (IPNS) converts delta-(L-alpha- aminoadipyl)-L-cysteinyl-D-valine (ACV) to isopenicillin N; an equimolar amount of oxygen is used in this oxidative ring closure reaction. Oxygen uptake rates of the reaction catalysed by partially purified IPNS from Penicillium chrysogenum SC 6140 and P2 were measured using an oxygen electrode. In contrast to published properties of Cephalosporium acremonium IPNS, the enzyme from P. chrysogenum was not stimulated by the addition of glutathione and showed reduced stimulation by Fe2+. The analysis of oxygen uptake rates showed the reaction to be first order with respect to oxygen concentration and the Km for ACV to be 0.4 mmol dm-3. The implications of these results for cell-free reactions using this enzyme and penicillin fermentations are discussed.