Methionine metabolism is a process that is necessary for humans. Methionine metabolism in mammals happens within two pathways, a methionine cycle and a transsulfuration sequence. These pathways have three common reactions with both pathways including the transformation of methionine to S-adenosylmethionine (SAM), the use of SAM in many different transmethylation reactions resulting in a methylated product plus S-adenosylhomocysteine, and the conversion of S-adenosylhomocysteine to produce the compounds homocysteine and adenosine. The reactions mentioned above not only produce cysteine, they also create a-ketobutyrate. This compound is then converted to succinyl-CoA through a three step process after being converted to propionyl-CoA. If the amino acids cysteine and methionine are available in enough quantity, the pathway will accumulate SAM and this will in turn encourage the production of cysteine and a-ketobutyrate, which are both glucogenic, through cystathionine synthase. When there is a lack of methionine, there is a decrease in the production of SAM, which limits cystathionine synthase activity.

Methionine Metabolism References