The breakdown of methionine in the body results in the production of Homocysteine. Methionine is converted by the action of the enzyme methionine adenosyltransferase (MAT) to S-adenosylmethionine (SAMe). This occurs in the normal pathway. The next phase after this is the hepatic phase II detoxification. In this phase, SAMe contributes a methyl group. It thus becomes S-adenosylhomocysteine (SAH).
This then becomes homocysteine after the loss of its adenosine. The recycling of homocysteine back to methionine must then occur. This takes place by accepting a methyl group from methylcobalmin. Methylcoblmin is recycled to methionine by the action of the addition of a methyl group to it. The methyl group is obtained from betaine. This is then converted into cysteine and taurine. This process takes place with the help of vitamins.