Comparative characterization of new glutaryl 7-ACA and cephalosporin C acylases

We performed a comparative characterization of three new cephalosporin acylases which were prepared from E. coli recombinant strains and found originally from Pseudomonas sp. A14, Bacillus laterosporus J1 and Pseudomonas diminuta N176. Both A14 and N176 acylases consisted of two non-identical subunits (α, β) whose molecular weights were 28,000 (α), 61,000 (β) and 26,000 (α), 58,000 (β), respectively, whereas J1 acylase consisted of a single peptide with molecular weight of 70,000. The maximum specific activities of A14, J1 and N176 acylases for glutaryl 7-ACA were 7.1, 5.3 and 100 units/mg, respectively, and that of N176 acylase for cephalosporin C was 3.1 units/mg. The K_m values of glutaryl 7-ACA for A14, J1 and N176 acylases were 2.1, 3.2 and 2.6 mM, respectively, and that of cephalosporin C for N176 acylase was 4.8 mM. A14, J1 and N176 acylases exhibited differential activities for cephalosporins having an aliphatic dicarboxylic acid in the acyl side chain and only N176 acylase showed an activity for cephalosporin C. N176 acylase as well as A14 acylase also showed a weak activity for a cephalosporin derivative having a heterocyclic carboxylic acid in the side chain. A14, J1 and N176 acylases catalyzed the reverse reaction to synthesize glutaryl 7-ACA from 7-ACA and glutaric acid, although the rate of the synthesis was 10 to 10⁵ fold slower than that of hydrolysis. The activities of the cephalosporin acylases were considerably inhibited by the reaction products, 7-ACA and glutaric acid. The types of the inhibition by 7-ACA and glutaric acid were both competitive. A14, J1 and N176 acylases were thermostable, their residual activities exceeding more than 90% after treatment at 50°C for 1 h at their optimal pHs.