Enzymic and Nonenzymic Cleavage of Trimethylamine-N-oxide in vitro at Subzero Temperatures

Abstract

Marine fish species such as the gadoid family contain a large amount of trimethylamine-N-oxide (TMAO) which is cleaved to equimolar amounts of dimethylamine (DMA) and formaldehyde (FA) during storage. The cleavage of TMAO was investigated at subzero temperatures in a model system containing Fe²⁺ and reductants, ascorbate and cysteine, in the presence or absence of TMAOase which was prepared from walleye pollack muscle. At -4°C in the supercooled solution, TMAO was cleaved to DMA and FA with TMAOase depending on enzyme concentration. Almost no nonenzymic cleavage occurred practically. However, in the frozen state at -4°C as well as at -20 and -40°C, the enzymic cleavage was completely depressed and DMA was rapidly and greatly produced by the nonenzymic pathway in a Fe²⁺ -Cys system accompanied by a little formation of trimethylamine. Both enzymic and nonenzymic reactions required only Fe²⁺ with reductants to maintain the reaction.