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Betaine-Homocysteine S-Methyltransferase: A ZINC metalloenzyme that catalyzes the transfer of a methyl group from BETAINE to HOMOCYSTEINE to produce dimethylglycine and METHIONINE, respectively. This enzyme is a member of a family of ZINC-dependent METHYLTRANSFERASES that use THIOLS or selenols as methyl acceptors.Glycine N-Methyltransferase: An enzyme that catalyzes the METHYLATION of GLYCINE using S-ADENOSYLMETHIONINE to form SARCOSINE with the concomitant production of S-ADENOSYLHOMOCYSTEINE.Betaine: A naturally occurring compound that has been of interest for its role in osmoregulation. As a drug, betaine hydrochloride has been used as a source of hydrochloric acid in the treatment of hypochlorhydria. Betaine has also been used in the treatment of liver disorders, for hyperkalemia, for homocystinuria, and for gastrointestinal disturbances. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1341)Methyltransferases: A subclass of enzymes of the transferase class that catalyze the transfer of a methyl group from one compound to another. (Dorland, 28th ed) EC 2.1.1.DNA (Cytosine-5-)-Methyltransferase: An enzyme that catalyzes the transfer of a methyl group from S-ADENOSYLMETHIONINE to the 5-position of CYTOSINE residues in DNA.Methylation: Addition of methyl groups. In histo-chemistry methylation is used to esterify carboxyl groups and remove sulfate groups by treating tissue sections with hot methanol in the presence of hydrochloric acid. (From Stedman, 25th ed)Protein Methyltransferases: Enzymes that catalyze the methylation of amino acids after their incorporation into a polypeptide chain. S-Adenosyl-L-methionine acts as the methylating agent. EC 2.1.1.O(6)-Methylguanine-DNA Methyltransferase: An enzyme that transfers methyl groups from O(6)-methylguanine, and other methylated moieties of DNA, to a cysteine residue in itself, thus repairing alkylated DNA in a single-step reaction. EC 2.1.1.63.Hyperhomocysteinemia: Condition in which the plasma levels of homocysteine and related metabolites are elevated (>13.9 ┬Ámol/l). Hyperhomocysteinemia can be familial or acquired. Development of the acquired hyperhomocysteinemia is mostly associated with vitamins B and/or folate deficiency (e.g., PERNICIOUS ANEMIA, vitamin malabsorption). Familial hyperhomocysteinemia often results in a more severe elevation of total homocysteine and excretion into the urine, resulting in HOMOCYSTINURIA. Hyperhomocysteinemia is a risk factor for cardiovascular and neurodegenerative diseases, osteoporotic fractures and complications during pregnancy.S-Adenosylmethionine: Physiologic methyl radical donor involved in enzymatic transmethylation reactions and present in all living organisms. It possesses anti-inflammatory activity and has been used in treatment of chronic liver disease. (From Merck, 11th ed)Vitamin B 12: A cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. INTRINSIC FACTOR is important for the assimilation of vitamin B 12.Folic Acid: A member of the vitamin B family that stimulates the hematopoietic system. It is present in the liver and kidney and is found in mushrooms, spinach, yeast, green leaves, and grasses (POACEAE). Folic acid is used in the treatment and prevention of folate deficiencies and megaloblastic anemia.Histone-Lysine N-Methyltransferase: An enzyme that catalyzes the methylation of the epsilon-amino group of lysine residues in proteins to yield epsilon mono-, di-, and trimethyllysine. EC 2.1.1.43.tRNA Methyltransferases: Enzymes that catalyze the S-adenosyl-L-methionine-dependent methylation of ribonucleotide bases within a transfer RNA molecule. EC 2.1.1.Lipotropic Agents: Endogenous factors or drugs that increase the transport and metabolism of LIPIDS including the synthesis of LIPOPROTEINS by the LIVER and their uptake by extrahepatic tissues.S-Adenosylhomocysteine: 5'-S-(3-Amino-3-carboxypropyl)-5'-thioadenosine. Formed from S-adenosylmethionine after transmethylation reactions.Protein-Arginine N-Methyltransferases: Enzymes that catalyze the methylation of arginine residues of proteins to yield N-mono- and N,N-dimethylarginine. This enzyme is found in many organs, primarily brain and spleen.Sarcosine: An amino acid intermediate in the metabolism of choline.DNA-Cytosine Methylases: Methylases that are specific for CYTOSINE residues found on DNA.