title: Use of aqueous two-phase systems for in situ extraction of water soluble antibiotics during their synthesis by enzymes immobilized on porous supports.
abstract: Yields of kinetically controlled synthesis of antibiotics catalyzed by penicillin G acylase from Escherichia coli (PGA) have been greatly increased by continuous extraction of water soluble products (cephalexin) away from the surroundings of the enzyme. In this way its very rapid enzymatic hydrolysis has been avoided. Enzymes covalently immobilized inside porous supports acting in aqueous two-phase systems have been used to achieve such improvements of synthetic yields. Before the reaction is started, the porous structure of the biocatalyst can be washed and filled with one selected phase. In this way, when the pre-equilibrated biocatalyst is mixed with the second phase (where the reaction product will be extracted), the immobilized enzyme remains in the first selected phase in spite of its possibly different natural trend. Partition coefficients (K) of cephalexin in very different aqueous two-phase systems were firstly evaluated. High K values were obtained under drastic conditions. The best K value for cephalexin (23) was found in 100% PEG 600-3 M ammonium sulfate where cephalexin was extracted to the PEG phase. Pre-incubation of immobilized PGA derivatives in ammonium sulfate and further suspension with 100% PEG 600 allowed us to obtain a 90% synthetic yield of cephalexin from 150 mM phenylglycine methyl ester and 100 mM 7-amino desacetoxicephalosporanic acid (7-ADCA). In this reaction system, the immobilized enzyme remains in the ammonium sulfate phase and hydrolysis of the antibiotic becomes suppressed because of its continuous extraction to the PEG phase. On the contrary, synthetic yields of a similar process carried out in monophasic systems were much lower (55%) because of a rapid enzymatic hydrolysis of cephalexin.
authors: Laboratorio de Tecnologia Enzimatica, Instituto de Catalisis, CSIC, Universidad Autonoma, Cantoblanco, 28049 Madrid, Spain.
authors: O
authors: O
authors: Hernandez-Justiz
authors: R
authors: R
authors: Fernandez-Lafuente
authors: M
authors: M
authors: Terreni
authors: J M
authors: JM
authors: Guisan
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000302:isolation & purification; D001709:Biotechnology / Q000379:methods; D002384:Catalysis; D002506:Cephalexin / Q000138:chemical synthesis* / Q000302:isolation & purification*; D002511:Cephalosporins / Q000138:chemical synthesis* / Q000302:isolation & purification; D004800:Enzymes, Immobilized; D004926:Escherichia coli / Q000201:enzymology; D007202:Indicators and Reagents; D007700:Kinetics; D010399:Penicillin Amidase / Q000378:metabolism*; D012995:Solubility; D014867:Water
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D004800:Enzymes, Immobilized; D007202:Indicators and Reagents; D014867:Water; D010399:Penicillin Amidase; D002506:Cephalexin