Immobilization of penicillin G acylase in layered double hydroxides pillared by glutamate ions

Immobilized penicillin G acylase (PGA) has been assembled in the interlayer galleries of a layered double hydroxide (LDH) by a three-step process. Glutamate-pillared LDH was first prepared by a novel process involving dissolution of an LDH-carbonate precursor in aqueous glutamic acid, followed by precipitation of the product by addition of base. This method avoids the problem of competitive intercalation by nitrate ions observed with conventional methods involving precipitation of LDHs from solutions of metal nitrate salts. The glutamate ions are strongly held in the interlayer region of the LDH by virtue of the electrostatic interaction between their carboxylate groups and the cationic layers, and act as carriers for the introduction and retention of free amino groups in the interlayer galleries. Subsequent reaction of the amino groups of the immobilized glutamate ions with a glutaraldehyde linker followed by addition of PGA affords the immobilized enzyme (IME). The intermediate and final materials, which can be termed bioinorganic nanocomposites, have been characterized by FT-IR spectra, powder X-ray diffraction (XRD) and thermal analysis. The activity, thermal stability, pH stability and operational stability of the IME have been assayed. After 10 recycles, carried out in succession in a discontinuous reactor, the IME displayed 90% activity retention, with the expressed activity remaining above 430 U/g.