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  Indian J Med Microbiol
 

Figure 1: Simplified schematic of the folate-dependent methionine cycle. Homocysteine (HCY) is converted into methionine by methionine synthase (MS), which utilizes vitamin B12 as a cofactor and acquires a methyl group from the active form of folate, 5-methyltetrahydrofolate (5-CH3-THF), which is subsequently converted to tetrahydrofolate (THF). Methionine is further converted to S-adenosylmethionine(SAM), through the activity of methionine adenosyl transferase. SAM is the major methyl donor for all methyltransferases, which adds methyl groups to various acceptor molecules such as DNA, RNA, phospholipids, and proteins. SAM is then converted to S-adenosylhomocysteine (SAH), which is reversibly converted to HCY in a reaction catalyzed by SAH-hydrolase. Based on MS activity and the availability of folate and vitamin B12, HCY is re-methylated back to methionine, as mentioned earlier

Figure 1: Simplified schematic of the folate-dependent methionine cycle. Homocysteine (HCY) is converted into methionine by methionine synthase (MS), which utilizes vitamin B12 as a cofactor and acquires a methyl group from the active form of folate, 5-methyltetrahydrofolate (5-CH3-THF), which is subsequently converted to tetrahydrofolate (THF). Methionine is further converted to S-adenosylmethionine(SAM), through the activity of methionine adenosyl transferase. SAM is the major methyl donor for all methyltransferases, which adds methyl groups to various acceptor molecules such as DNA, RNA, phospholipids, and proteins. SAM is then converted to S-adenosylhomocysteine (SAH), which is reversibly converted to HCY in a reaction catalyzed by SAH-hydrolase. Based on MS activity and the availability of folate and vitamin B12, HCY is re-methylated back to methionine, as mentioned earlier