Abstract
Cephalexin was synthesized in aqueous two-phase systems (ATPSs) by using penicillin G acylase (PGA) (penicillin amidohydrolase, EC3.5.1.11) as a catalyst and 7-aminodeacetoxicephalosporanic acid (7-ADCA) and phenylglycine methyl ester (PGME) as substrates. In the ATPS composed of 20% (w/w) PEG 400 and 15% (w/w) magnesium sulfate, the partition coefficient of PGA ( K E) was less than 0.01, PGA biased to the magnesium sulfate-rich bottom phase. The partition coefficient of cephalexin ( K C) was 6.7, and the partition coefficients of PGME ( K P) and 7-ADCA ( K A) were 1.5 and 1.2, respectively. The stability of PGA in 20% (w/w) PEG 400 and 15% (w/w) magnesium sulfate ATPS was investigated. The activity of PGA was remained 80.6% after PGA was retained in the ATPS for 35 h and reserved 59% in the 20% magnesium sulfate solution at pH 7.0. When free enzyme was used for bioconversion, a high yield of cephalexin (60%) was achieved at the concentration of 100 mM 7-ADCA and 100 mM PGME in this ATPS than that of in an aqueous system (21%).
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