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A mutant strain with high penicillin G acylase activity was derived from Escherichia coli ATCC 11105 by chemical mutagenesis, using N‐methyl‐N′‐nitro‐N‐nitrosoguanidine. Penicillin acylase was extracted from the mutant strain and highly purified by DEAE‐cellulose and hydroxyapatite column chromatography followed by preliminary precipitation steps. Vm and Km values of the enzyme (specific activity: 24·81 U mg−1, protein concentration: 0.56 mg cm−3) were found to be 22.73 U cm−3 mm−1 and 3.18 mmold m−3 penicillin G, respectively. The enzyme was shown to be uncompetitively inhibited by excess of substrate. The inhibition by phenylacetic acid was found to be competitive, and 6‐aminopenicillanic acid to be noncompetitive. Inhibition constants for excess of penicillin G, phenylacetic acid and 6‐aminopenicillanic acid were estimated as 74.20, 18.74 and 15.00 mmol dm−3 respectively, at pH 8.0 and 40°C. The activation energy of the enzymatic hydrolysis reaction of penicillin G was found to be 10.78 kcal mol−1. Optimal pH and temperature values of the enzyme were determined as 8.0 and 60°C. Complete loss of the enzyme stability occurred when the enzyme was incubated at pH 10.0 for 2 days or at 50°C for 2 h.

A B S T R A C T Highly purifiedpenicillin G acylase from a tnutant derivative

A B S T R A C TEmulsification of natural oils by a surfactant increases their eficiency as chemical antifoams. The presence of low concentrations of fatty acids or other surfactants have been reported to inhibit or stimulate microbial growth andlor product formation.The effects of different natural oils, Tween 80 and saponin on growth and cellulase production by T. reesei and S. pulverulentum have been investigated. It was ,found that in general, emulsification leads to higher cellulase activities in both cultures, though there are variations in enzyme levels depending on the presence or absence of Tween 80 and of different oils in growth media as well as the substrates used for cellulase assay.

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