Aspartate aminotransferases (AspAT) can catalyze the reversible transamination reaction from aspartate to α-ketoglutarate to form glutamate and oxaloacetate. T. thermophilus AspAT (TtAspAT) has been cloned from HB8 by Okamoto et al. (67) and crystal structure has been resolved by Nakai et al.(64). It presents a substrate preference of amino acids with carboxyl group (aspartate and glutamate) and also found to possess significant activity against aromatic amino acids and branched-chain amino acids. Our previous study showed that TtAspAT have the ability to catalyze the synthesis of L-homophenylalanine, which is an important compound in the synthesis of anti-hypertensive drugs, the angiotensin-converting enzyme (ACE) inhibitors. TtAspAT is of advantage in high thermostabilty and having better activity than E. coli AspAT.
The objective of this study was to investigate the best condition to synthesis L-homophenylalnine (L-HPA) using TtAspAT and L-Glutamate as a substrate. This enzyme was also test for its activity against monosodium glutamate (MSG) in synthesizing L-homophenylalanine (L-HPA), since MSG is the cheapest amino acid in food industry. In this study, TtAspAT showed the better activity on Tris-HCl buffer than Bis-Tris Propane against L-Glutamate. Significant effect was observed in terms of Tm, pH, L-Glutamate and D-Alanine. Bioconversion of homophenylalanine was conducted at 60°C at different intervals and showed the highest rate after 15-hour incubation.
