Catalyzes the transfer of a methyl group from methyl- cobalamin to homocysteine, yielding enzyme-bound cob(I)alamin and methionine. Subsequently, remethylates the cofactor using methyltetrahydrofolate. Defects in MTR are the cause of methylcobalamin deficiency type G (cblG); also known as homocystinuria-megaloblastic anemia complementation type G. It is an autosomal recessive inherited disease that causes mental retardation, macrocytic anemia, and homocystinuria. Mild deficiency in MS activity could be associated with mild hyperhomocysteinemia, a risk factor for cardiovascular disease and possibly neural tube defects. MS mutations could also be involved in tumorigenesis. Defects in MTR may be a cause of susceptibility to folate-sensitive neural tube defects (FS-NTD). The most common NTDs are open spina bifida (myelomeningocele) and anencephaly. Genetic defects in MTR may affect the risk of spina bifida via the maternal rather than the embryonic genotype. Belongs to the vitamin-B12 dependent methionine synthase family. Note: This description may include information from UniProtKB.
Protein type: Amino Acid Metabolism - cysteine and methionine; Cofactor and Vitamin Metabolism - one carbon pool by folate; EC 126.96.36.199; Methyltransferase