Distribution and some characteristics of trimethylamine N-oxide (TMAO) demethylase activity of red hake muscle.
Phillippy B.Q. | Hultin H.O.
It has been suggested by some workers that decomposition of trimethyl N-oxide (TMAO) to dimethylamine (DMA) and formaldehyde in gadoid fishes occurs via enzymic processes while others have suggested a nonenzymic pathway. DMA production in frozen red hake muscle is shown in this study to be enzymic by the necessity of the high molecular weight soluble or insoluble fraction from red hake to convert the low molecular weight components of flounder muscle to DMA. In red hake muscle the TMAO demethylase activity is approximately evenly divided between the high molecular weight soluble and the insoluble fractions: the amount of potential activity in either fraction is 60-100 times that required for the production of DMA that normally occurs during frozen storage of the muscle tissue. The Km for TMAO of the soluble enzyme was approximately 3 mM; the concentrations of TMAO in red hake muscle range from 60 to 140 mM (calculation based on water content of 80%). Thus, it seems unlikely that TMAO or TMAO demethylase limit the rate of the reaction. On the other hand, the Km values for flavin mononucleotide and NADH are higher than the concentrations of these components found in the tissue suggesting that the cofactors limit the rate of TMAO breakdown to DMA and formaldehyde in the stored muscle. This supports other studies (Landolt and Hultin 1982; Banda and Hultin 1983) in which the same conclusion is reached based on other considerations.
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