【涵涵（邀請碼107252）】評論

In the “Biochemistry” textbook and several reports as below mentioned that S-adenosyl-L-methionine (SAM) is a universal methyl donor for various molecules, such as DNA, protein, metabolite as shown below.Serine provides methylene group for tetrahydrofolate(THF) to generate N5, N10-methylene tetrahydrofolate, which serves as a methyl donor for dUMP, Thus, serine is not a common methyl donor.Reference: Biochemistry, by Roger Miesfeld and Megan McEvoy, 2017 (ISBN:9780393977264), page 331-332, 886-887. 930 (legend of figure 18.33)Nicotinamide N-Methyltransferase Interacts with Enzymes of the Methionine Cycle and Regulates Methyl Donor Metabolism.Biochemistry 2018, 57, 40, 5775–5779The Role of Methyl Donors of the Methionine Cycle in Gastrointestinal Infection and Inflammation. Healthcare vol. 10,1 61. 29 Dec. 2021, 維持原公布答案(A)