l-Phenylalanine synthesis catalyzed by immobilized aspartate aminotransferase

The essential amino acid l-phenylalanine (Phe), extensively applied in the manufacture of food and drink products, is usually produced by chemoenzymatic or fermentative processes. In this work, an enzymatic alternative based on the application of the enzyme l-aspartate aminotransferase (AAT; EC 2.6.1.1) from porcine heart, which catalyzes the transamination between phenylpyruvate and l-aspartate, was developed. Aiming to improve its stability and enable the reuse, the enzyme AAT was immobilized via different techniques such as by covalent attachment on Eupergit® C (epoxy support) and MANA-agarose (amino support), and by entrapment in polyvinyl alcohol hydrogel particles (LentiKats®). For low enzymatic loads, retained activities of 40, 70 and 40% and immobilization yields of 95, 98 and 40% were obtained using Eupergit® C, MANA-agarose and LentiKats®, respectively. Free and highly loaded immobilized enzymes were used to synthesize l-phenylalanine. The high conversions, reaction yields and initial rates obtained for free enzyme were similar to those obtained when using Eupergit® C and LentiKats® immobilized catalysts. Moreover, the AAT stability under reaction conditions was moderately enhanced for Eupergit® C and LentiKats® immobilized enzymes related to that of the free enzyme.