Betaine-Homocysteine-Methyl-Transferases. I. Distribution in Nature.

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Abstract
Various types of living material have been homogenized and incubated with betaine and homocysteine in order to test their ability to form methionine by means of methyl group transfer. Enzymes that catalyze this reaction are called betaine-homocysteine-methyl-transferases and were found in the livers of all the vertebrates investigated, ranging from Homo sapiens to Petromyzon fluviatilis. These enzymes were not found in appreciable amounts in any other vertebrate organ except in the kidney of the guinea pig. The only non-vertebrate in which a betaine -homocysteine-methyl-transferase has been detected so far is the pond mussel Anodonta cygnea 4. Methyl transferases were not found in plants and microorganisms. The transferases were partially purified from some materials. Dimethyl-[beta]-propiothetin but not choline could replace betaine as methyl group donor in all cases tested. Dimethylglycine but not choline markedly inhibited the transfer reaction. The methyl-transferase of human liver was much more stable to heat than that of pike liver. The apparent pH-optima of the transferases studied varied from about 7.0 for pike to about 8.5 for pond mussel. Only L-homo-cysteine seemed to be methylated.