Functional characterization of Capsicum chinense vanillin aminotransferase: Detection of vanillylamine-forming...

In capsaicin biosynthesis, vanillin aminotransferase (VAMT; EC 2.6.1.119) catalyzes the conversion of vanillin (V) to vanillylamine (VA). In vitro analysis of the recombinant VAMT enzyme has been reported; however, this enzyme catalyzed only the V-forming reaction and not the VA-forming reaction, which is inconsistent with the postulated pathway for capsaicin biosynthesis. In this study, we expressed, purified, and characterized functional recombinant VAMT of Capsicum chinense cv. Habanero from an Escherichia coli strain. The enzyme catalyzed reversible transamination between V and VA, and its VA-forming activity was high when γ-aminobutyric acid (GABA) was used as an amino donor. The enzyme exhibited maximum activity at pH 8.0 and 55 °C, and was stable up to 60 °C over a pH range from 4.5 to 8.0. The enzyme was stable in the presence of various chemicals and metal ions. The enzyme accepted several 4-8-carbon long primary amines and ω-amino acids with carbon chains longer than 4 as amino donors despite the narrow specificity of the amino acceptor. Based on its kinetic attributes and localization, VAMT appears to have evolved from GABA-aminotransferase to catalyze reversible transamination between V and VA, and is responsible for VA biosynthesis using GABA as an amino donor in the cytosol of capsicum fruit cells.