What is the SAM cycle?

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]