¥â-Lactmase was isolated from the culture filtrate of the penicillin producing strain, Penicillium chrysogenum Q176. When the pH of the medium was adjusted to 5.0 at the start of culture, a rapid increase in pH accompanied by the synthesis of penicillin was observed in the first 2¡4 days. When the pH of medium was brought to 6.0 or 7.0 the opposite was observed: high yield of the enzyme and little of the antibiotics in the medium. The optimum enzyme activity was at a temperature of 40¡É and around pH 7.0. A partially purified enzyme was assayed on several different substrates including penicillins V and G, 6-aminopenicillanic acid, cephalosporin C. The V_(max) values calculated were 24.5, 20.4, 7.6, .and 0.1 mmoles/hour, and the K_m values were 16.4, 12.6, 7.5, and 6.9 mM in the order given.
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