DISTRIBUTION AND SOME CHARACTERISTICS OF TRIMETHYLAMINE N-OXIDE (TMAO) DEMETHYLASE ACTIVITY OF RED HAKE MUSCLE

It has been suggested by some workers that decomposition of trimethyl N-oxide (TMAO) to dimethylamine (DMA) and formaldehyde in gadoid fishe s occurs via enzymic processes while others have suggested a nonenzymi c pathway. DMA production in frozen red hake muscle is shown in this s tudy to be enzymic by the necessity of the high molecular weight solub le or insoluble fraction from red hake to convert the low molecular we ight 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 p otential activity in either fraction is 60-100 times that required for the production of DMA that normally occurs during frozen storage of t he muscle tissue. The K(M) for TMAO of the soluble enzyme was approxim ately 3 mM; the concentrations of TMAO in red hake muscle range from 6 0 to 140 mM (calculation based on water content of 80%). Thus, it seem s unlikely that TMAO or TMAO demethylase limit the rate of the reactio n. On the other hand, the K(M) values for flavin mononucleotide and NA DH 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 stu dies (Landolt and Hultin 1982; Banda and Hultin 1983) in which the sam e conclusion is reached based on other considerations.