The catalytic properties of penicillin G acylase (PGA) from Escherichia coli in kinetically controlled synthesis of β-lactam antibiotics are negatively affected upon immobilization on hydrophobic acrylic carriers. Two strategies have been here pursued to improve the synthetic performance of PGA immobilized on epoxy-activated acrylic carriers. First, an aldehyde-based spacer was inserted on the carrier surface by glutaraldehyde activation (immobilization yield = 50%). The resulting 3-fold higher synthesis/hydrolysis ratio (vs/vh1 = 9.7 ± 0.7 and 10.9 ± 0.7 for Eupergit® C and Sepabeads® EC-EP, respectively) with respect to the unmodified support (vs/vh1 = 3.3 ± 0.4) was ascribed to a facilitated diffusion of substrates and products as a result of the increased distance between the enzyme and the carrier surface. A second series of catalysts was prepared by direct immobilization of PGA on epoxy-activated acrylic carriers (Eupergit® C), followed by quenching of oxiranes not involved in the binding with the protein with different nucleophiles (amino acids, amines, amino alcohols, thiols and amino thiols). In most cases, this derivatization increased the synthesis/hydrolysis ratio with respect to the non derivatized carrier. Particularly, post-immobilization treatment with cysteine resulted in about 2.5-fold higher vs/vh1 compared to the untreated biocatalyst, although the immobilization yield decreased from 70% (untreated Eupergit® C) to 20%. Glutaraldehyde- and cysteine-treated Eupergit® C catalyzed the synthesis of cefazolin in 88% (±0.9) and 87% (±1.6) conversion, respectively, whereas untreated Eupergit® C afforded this antibiotic in 79% (±1.2) conversion.
大肠杆菌
青霉素G酰化酶(
PGA)的催化性质在动力学控制的β-内酰胺抗生素合成中,当其固定在疏
水性
丙烯酸载体上时会受到负面影响。本文采用两种策略来提高
PGA固定在环氧活化
丙烯酸载体上的合成性能。首先,通过
戊二醛活化在载体表面插入基于醛基的间隔臂(固定化产率为50%)。与未修饰的载体相比,所得到的合成/
水解比(vs/vh1)提高了3倍(分别为Eupergit® C和Sepabeads®
EC-EP的9.7±0.7和10.9±0.7),这归因于由于酶与载体表面之间的距离增加,使得底物和产物的扩散更加容易。第二种催化剂系列是通过将
PGA直接固定在环氧活化的
丙烯酸载体(Eupergit® C)上,然后使用不同亲核试剂(
氨基酸、胺、
氨基醇、
硫醇和
氨基
硫醇)淬灭未与蛋白质结合的
环氧乙烷来制备的。在大多数情况下,这种衍生化相比于非衍生化载体增加了合成/
水解比。特别是,用半胱
氨酸进行后固定化处理使得vs/vh1比未处理的
生物催化剂提高了约2.5倍,尽管固定化产率从70%(未处理的Eupergit® C)降至20%。经过
戊二醛和半胱
氨酸处理的Eupergit® C催化
头孢唑啉的合成转化率分别为88%(±0.9)和87%(±1.6),而未处理的Eupergit® C则达到79%(±1.2)的转化率。