MTR (5-Methyltetrahydrofolate-Homocysteine Methyltransferase): MTR is a key enzyme involved in the remethylation pathway of homocysteine metabolism. It catalyzes the transfer of a methyl group from 5-methyltetrahydrofolate (5-MTHF) to homocysteine, producing methionine and tetrahydrofolate (THF). Methionine serves as a precursor for S-adenosylmethionine (SAM), a universal methyl donor essential for various methylation reactions in the body, including DNA methylation, neurotransmitter synthesis, and histone modification. Proper MTR activity is crucial for maintaining normal homocysteine levels and supporting cellular methylation processes. Dysregulation of MTR, often caused by genetic mutations or deficiencies, can disrupt these critical functions.