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Pathway Description
Methionine Metabolism
Homo sapiens
Metabolic Pathway
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.
References
Methionine Metabolism References
Lehninger, A.L. Lehninger principles of biochemistry (4th ed.) (2005). New York: W.H Freeman.
Salway, J.G. Metabolism at a glance (3rd ed.) (2004). Alden, Mass.: Blackwell Pub.
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