The S-adenosylmethionine (SAM) cycle is a series of metabolic steps that produce, break down, and regenerate S-adenosylmethionine.[1][2][3] The SAM cycle converts S-adenosylmethionine to S-adenosylhomocysteine to homocysteine to methionine and back to S-adenosylmethionine using various enzymes.[1][2][3] The enzymatic conversion of homocysteine to methionine in the SAM cycle uses vitamin B12 as a cofactor and links the SAM cycle to the folate cycle to make up a complex series of metabolic pathways known as one-carbon metabolism.[4] It is called one-carbon metabolism because these processes produce and provide one-carbon methyl groups (CH3) for several important biological processes (DNA synthesis, DNA methylation, immune function, amino acid metabolism, etc.).[1][2][3][4]
What is the SAM cycle?
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•Last Updated: May 16, 2025
The SAM cycle is a series of metabolic steps that produce, break down, and regenerate S-adenosylmethionine and involve the conversion of S-adenosylmethionine to S-adenosylhomocysteine, homocysteine, and methionine, with vitamin B12 as a cofactor. This cycle is part of one-carbon metabolism, which provides methyl groups for essential biological processes such as DNA synthesis and amino acid metabolism.