Enzymatic synthesis of β‐lactam antibiotics using penicillin‐G acylase in frozen media

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Abstract
Penicillin‐G acylase (EC 3.5.1.11) fromEscherichia colicatalyzed the synthesis of various β‐lactam antibiotics in ice at −20°C with higher yields than obtained in solution at 20°C. The initial ratio between aminolysis and hydrolysis of the acyl‐enzyme complex in the synthesis of cephalexin increased from 1.3 at 20°C to 25 at −20°C. The effect on the other antibiotics studied was less, leading us to conclude that freezing of the reaction medium influences the hydrolysis of each nucleophile‐acyl‐enzyme complex to a different extent. Only free penicillin‐G acylase could perform transformations in frozen media: immobilized preparations showed a low, predominantly hydrolytic activity under these conditions.