Figure 2.

Effect of FeSO₄ concentration on ring expansion of penicillin G by resting cells. The concentration of FeSO₄ previously used for unsuccessful cell-free ring expansion of penicillin G was 0.04 (10). Reaction contained 50 mM Tris⋅HCl (pH 7.4), 1.28 mM α-ketoglutarate, 4 mM ascorbic acid, and 2 mg/ml penicillin G. Dry cell weight was 10 mg/ml. Samples were taken at 2 h and were centrifuged (14,000 × g, 5 min); 200 μl was used in the bioassay.