Cephalexin synthesis by partially purified and immobilized enzymes

Abstract

An enzyme which catalyzes the synthesis of cephalexin from D-$\alpha$-Phenylglycine methylester (PGM) and 7-amino-3 desacetoxy cephalosporanic acid (7-ADCA) was prepared from $\mbox{\underline{Xanthomonas}}$ $\mbox{\underline{citri}}$ IFO 3835, and partially purified 30-fold by ammonium sulfate fractionation, DEAE-cellulose, and Sepharose-4B column chromatography. This enzyme preparation was immobilized onto the several adsorbents by adsorption. Among these, kaolin and bentonite showed a high enzyme activity retention and reusing stability. Activity retentions of enzyme adsorbed onto kaolin and bentonite were determined as 92\% and 71\%, respectively. The biochemical properties of immobilized enzyme, such as optimum temperature, pH, and kinetic constants, were investigated and compared with those of the soluble enzyme. Optimum temperature, PH and Km values for 7-ADCA, PGM and cephalexin of soluble enzyme were determined as 35$^\circ$C, PH 6.2, 11.1mM, 2.1mM, and 1.61mM, respectively. These parameters of immobilized enzyme were also determined as 37$^\circ$C, PH 6.2, 11.5mM, 2.1mM, and 2.0mM, respectively. From the experimental results of kinetics and substrate mole ratio effect on conversion, it was found that the final equilibrium concentrations of cephalexin were influenced by the initial mole ratio of substrates. Therefore, 85\% mole base conversion of substrates to product could be obtained at the mole ratio of 1:3 within 2 hr. Based on the experimental results, we concluded that the cephalexin synthetic reaction was considered to be reversible bi-uni reaction. Model of a rate equation was derived to describe the enzymatic synthesis of cephalexin. The integrated form of the rate equation has shown to predict satisfactorily the progress of the reaction in a batch reactor. There was a good agreement between the experimental results and the theoretical analyses performed by computer simulation.