Enzymatic production of 5′-inosinic acid by a newly synthesised acid phosphatase/phosphotransferase

5′-Nucleotides including 5′-inosinic acid have characteristic taste and important application in various foods as flavour potentiators. The selective nucleoside acid phosphatase/phosphotransferase (AP/PTase) can catalyse the synthesis of 5′-nucleotides by transfer of phosphate groups. In this study, a 747-bp gene encoding AP/PTase from Escherichia blattae was synthesised. After expression, the recombinant AP/PTase was purified using nickel–NTA. The optimal temperature and pH of this enzyme were 30 °C and 5.0, respectively. The activity was partially inhibited by metal ions such as Hg2+, Ag+ and Cu2+, but not by chelating reagents such as EDTA. The values of Km and Vmax for inosine were 40 mM and 3.5 U/mg, respectively. Using this purified enzyme, 16.83 mM of 5′-IMP was synthesised from 37 mM of inosine and the molar yield reached 45.5%. Homology modelling and docking simulation were discussed.