Novel insights into the inhibitory mechanism of (+)-catechin against trimethylamine-N-oxide demethylase

Trimethylamine-N-oxide demethylase (TMAOase) is a key enzyme for the decomposition of trimethylamine oxide into formaldehyde. The study investigated the inhibitory effects of (+)-catechin on TMAOase and involved mechanism to minimize the formaldehyde (FA) content of seafood during storage. TMAOase was purified by DEAE-52 cellulose and Sephacryl S-300 chromatography and the inhibitory mechanism of TMAOase was studied by Lineweaver-Burk plots, fluorescence spectroscopy, and circular dichroism. Specific activity of 37 ± 0.7 U/mg was obtained with 205 -fold purification and 15% yield, and molecular mass was 25 kDa. (+)-Catechin was a reversible inhibitor of TMAOase and its induced mechanism was the non-competitive inhibition type. (+)-Catechin binding to TMAOase formed a complex with the binding constant (Ksv) of 0.72 × 103 at 298 K. The formation of complex induced the static fluorescence quenching and changes in the conformation of TMAOase, leading to a reduction in the rate of catalysis.