Betaine—homocysteine S-methyltransferase

In the field of enzymology, a betaine-homocysteine S-methyltransferase also known as betaine-homocysteine methyltransferase (BHMT) is a zinc metallo-enzyme that catalyzes the transfer of a methyl group from trimethylglycine and a hydrogen ion from homocysteine to produce dimethylglycine and methionine respectively:^[2]

Trimethylglycine (methyl donor) + homocysteine (hydrogen donor) → dimethylglycine (hydrogen receiver) + methionine (methyl receiver)

Diagram of the action of BHMT

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. This enzyme participates in the metabolism of glycine, serine, threonine and also methionine.

Isozymes

In humans, there are two isozymes, BHMT^[3]^[4] and BHMT2,^[5]^[6] each encoded by a separate gene.

betaine-homocysteine methyltransferase
Identifiers
Symbol	BHMT
Entrez	635
HUGO	1047
OMIM	602888
RefSeq	NM_001713
UniProt	Q93088
Other data
EC number	2.1.1.5
Locus	Chr. 5 q13.1-q15

betaine-homocysteine methyltransferase 2
Identifiers
Symbol	BHMT2
Entrez	23743
HUGO	1048
OMIM	605932
RefSeq	NM_017614
UniProt	Q9H2M3
Other data
EC number	2.1.1.5
Locus	Chr. 5 q13

Tissue distribution

BHMT is expressed most predominantly in the liver and kidney.^[7]

Clinical significance

Anomalies in homocysteine metabolism have been implicated in disorders ranging from vascular disease, autism, and schizophrenia to neural tube birth defects such as spina bifida.

References

↑ PDB: 1UMY; González B, Pajares MA, Martínez-Ripoll M, Blundell TL, Sanz-Aparicio J (May 2004). "Crystal structure of rat liver betaine homocysteine s-methyltransferase reveals new oligomerization features and conformational changes upon substrate binding". J. Mol. Biol. 338 (4): 771–82. doi:10.1016/j.jmb.2004.03.005. PMID 15099744.
↑ Pajares MA, Pérez-Sala D (December 2006). "Betaine homocysteine S-methyltransferase: just a regulator of homocysteine metabolism?". Cell. Mol. Life Sci. 63 (23): 2792–803. doi:10.1007/s00018-006-6249-6. PMID 17086380.
↑ Garrow TA (September 1996). "Purification, kinetic properties, and cDNA cloning of mammalian betaine-homocysteine methyltransferase". J. Biol. Chem. 271 (37): 22831–8. PMID 8798461.
↑ Sunden SL, Renduchintala MS, Park EI, Miklasz SD, Garrow TA (September 1997). "Betaine-homocysteine methyltransferase expression in porcine and human tissues and chromosomal localization of the human gene". Arch. Biochem. Biophys. 345 (1): 171–4. doi:10.1006/abbi.1997.0246. PMID 9281325.
↑ Chadwick LH, McCandless SE, Silverman GL, Schwartz S, Westaway D, Nadeau JH (November 2000). "Betaine-homocysteine methyltransferase-2: cDNA cloning, gene sequence, physical mapping, and expression of the human and mouse genes". Genomics. 70 (1): 66–73. doi:10.1006/geno.2000.6319. PMID 11087663.
↑ Szegedi SS, Castro CC, Koutmos M, Garrow TA (April 2008). "Betaine-homocysteine S-methyltransferase-2 is an S-methylmethionine-homocysteine methyltransferase". J. Biol. Chem. 283 (14): 8939–45. doi:10.1074/jbc.M710449200. PMC 2276374. PMID 18230605.
↑ Sunden SL, Renduchintala MS, Park EI, Miklasz SD, Garrow TA (September 1997). "Betaine-homocysteine methyltransferase expression in porcine and human tissues and chromosomal localization of the human gene". Arch. Biochem. Biophys. 345 (1): 171–4. doi:10.1006/abbi.1997.0246. PMID 9281325.

External links

Betaine Homocysteine Methyltransferase at the US National Library of Medicine Medical Subject Headings (MeSH)
EC 2.1.1.5

Metabolism: Protein metabolism, synthesis and catabolism enzymes

Essential amino acids are in Capitals

K→acetyl-CoA

LYSINE→	Saccharopine dehydrogenase Glutaryl-CoA dehydrogenase

LEUCINE→	Branched chain aminotransferase Branched-chain alpha-keto acid dehydrogenase complex Isovaleryl coenzyme A dehydrogenase Methylcrotonyl-CoA carboxylase Methylglutaconyl-CoA hydratase 3-hydroxy-3-methylglutaryl-CoA lyase

TRYPTOPHAN→	Indoleamine 2,3-dioxygenase/Tryptophan 2,3-dioxygenase Arylformamidase Kynureninase 3-hydroxyanthranilate oxidase Aminocarboxymuconate-semialdehyde decarboxylase Aminomuconate-semialdehyde dehydrogenase

PHENYLALANINE→tyrosine→	(see below)

G→pyruvate
→citrate

glycine→serine→	Serine hydroxymethyltransferase Serine dehydratase glycine→creatine: Guanidinoacetate N-methyltransferase Creatine kinase

alanine→	Alanine transaminase

cysteine→	D-cysteine desulfhydrase

threonine→	L-threonine dehydrogenase

G→glutamate→
α-ketoglutarate

HISTIDINE→	Histidine ammonia-lyase Urocanate hydratase Formiminotransferase cyclodeaminase

proline→	Proline oxidase Pyrroline-5-carboxylate reductase 1-Pyrroline-5-carboxylate dehydrogenase/ALDH4A1 PYCR1

arginine→	Ornithine aminotransferase Ornithine decarboxylase Agmatinase

→alpha-ketoglutarate→TCA	Glutamate dehydrogenase

Other	cysteine+glutamate→glutathione: Gamma-glutamylcysteine synthetase Glutathione synthetase Gamma-glutamyl transpeptidase glutamate→glutamine: Glutamine synthetase Glutaminase

G→propionyl-CoA→
succinyl-CoA

VALINE→	Branched chain aminotransferase Branched-chain alpha-keto acid dehydrogenase complex Enoyl-CoA hydratase 3-hydroxyisobutyryl-CoA hydrolase 3-hydroxyisobutyrate dehydrogenase Methylmalonate semialdehyde dehydrogenase

ISOLEUCINE→	Branched chain aminotransferase Branched-chain alpha-keto acid dehydrogenase complex 3-hydroxy-2-methylbutyryl-CoA dehydrogenase

METHIONINE→	generation of homocysteine: Methionine adenosyltransferase Adenosylhomocysteinase regeneration of methionine: Methionine synthase/Homocysteine methyltransferase Betaine-homocysteine methyltransferase conversion to cysteine: Cystathionine beta synthase Cystathionine gamma-lyase

THREONINE→	Threonine aldolase

→succinyl-CoA→TCA	Propionyl-CoA carboxylase Methylmalonyl CoA epimerase Methylmalonyl-CoA mutase

G→fumarate

PHENYLALANINE→tyrosine→	Phenylalanine hydroxylase Tyrosine aminotransferase 4-Hydroxyphenylpyruvate dioxygenase Homogentisate 1,2-dioxygenase Fumarylacetoacetate hydrolase tyrosine→melanin: Tyrosinase

G→oxaloacetate

asparagine→aspartate→	Asparaginase/Asparagine synthetase Aspartate transaminase

Transferase: one carbon transferases (EC 2.1)

2.1.1: Methyl-

N-	Histamine N-methyltransferase Phenylethanolamine N-methyltransferase Amine N-methyltransferase Phosphatidylethanolamine N-methyltransferase

O-	5-hydroxyindole-O-methyltransferase/Acetylserotonin O-methyltransferase Catechol-O-methyl transferase

Homocysteine	Betaine-homocysteine methyltransferase Homocysteine methyltransferase Methionine synthase

Other	Phosphatidyl ethanolamine methyltransferase DNMT3B Histone methyltransferase Thymidylate synthase DNA methyltransferase Thiopurine methyltransferase

2.1.2: Hydroxymethyl-,
Formyl- and Related

Hydroxymethyltransferase	Serine hydroxymethyltransferase 3-methyl-2-oxobutanoate hydroxymethyltransferase

Formyltransferase	Phosphoribosylglycinamide formyltransferase Inosine monophosphate synthase

Other	Glutamate formimidoyltransferase Aminomethyltransferase

2.1.3: Carboxy-
and Carbamoyl

Carboxy	methylmalonyl-CoA carboxytransferase

Carbamoyl	Aspartate carbamoyltransferase Ornithine carbamoyltransferase Oxamate carbamoyltransferase Putrescine carbamoyltransferase 3-hydroxymethylcephem carbamoyltransferase Lysine carbamoyltransferase N-acetylornithine carbamoyltransferase

2.1.4: Amidine

Arginine:glycine amidinotransferase

Enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list)

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