Dopamine beta-hydroxylase

Dopamine beta-hydroxylase (DBH), also known as dopamine beta-monooxygenase, is an enzyme (EC 1.14.17.1) that in humans is encoded by the DBH gene. Dopamine beta-hydroxylase catalyzes the conversion of dopamine to norepinephrine.

Dopamine is converted to norepinephrine by the enzyme dopamine β-hydroxylase; ascorbic acid serves as a cofactor

DBH
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 4ZEL
Identifiers
Aliases	DBH, DBM, Dopamine beta-monooxygenase, dopamine beta-hydroxylase, Dopamine β-hydroxylase, ORTHYP1
External IDs	OMIM: 609312; MGI: 94864; HomoloGene: 615; GeneCards: DBH; OMA:DBH - orthologs
EC number	1.14.17.1
Gene location (Human) Chr. Chromosome 9 (human)[1] Band 9q34.2 Start 133,636,363 bp[1] End 133,659,329 bp[1]
Gene location (Mouse) Chr. Chromosome 2 (mouse)[2] Band 2 A3|2 19.29 cM Start 27,055,245 bp[2] End 27,073,212 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right lobe of liver right adrenal gland left adrenal gland left adrenal cortex sympathetic trunk superior vestibular nucleus right adrenal cortex lymph node body of pancreas granulocyte Top expressed in superior cervical ganglion adrenal gland external carotid artery tunica adventitia of aorta parasympathetic nervous system carotid body submandibular gland parasympathetic ganglion myocardium of ventricle secondary oocyte More reference expression data BioGPS More reference expression data
Gene ontology Molecular function metal ion binding monooxygenase activity oxidoreductase activity oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, reduced ascorbate as one donor, and incorporation of one atom of oxygen L-ascorbic acid binding catalytic activity dopamine beta-monooxygenase activity copper ion binding Cellular component cytoplasm transport vesicle membrane integral component of membrane chromaffin granule lumen chromaffin granule membrane cytoplasmic vesicle membrane extracellular region extracellular space secretory granule membrane secretory granule lumen intracellular membrane-bounded organelle endoplasmic reticulum microtubule organizing center Biological process response to amphetamine chemical synaptic transmission homoiothermy leukocyte mediated immunity visual learning fear response behavioral response to ethanol locomotory behavior regulation of extrinsic apoptotic signaling pathway regulation of cell population proliferation positive regulation of vasoconstriction glucose homeostasis maternal behavior memory leukocyte migration response to pain blood vessel remodeling cytokine production associative learning catecholamine biosynthetic process dopamine catabolic process norepinephrine biosynthetic process octopamine biosynthetic process positive regulation of cold-induced thermogenesis Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 1621 13166 Ensembl ENSG00000123454 ENSMUSG00000000889 UniProt P09172 Q64237 RefSeq (mRNA) NM_000787 NM_138942 RefSeq (protein) NP_000778 NP_620392 Location (UCSC) Chr 9: 133.64 – 133.66 Mb Chr 2: 27.06 – 27.07 Mb PubMed search [3] [4]
Wikidata
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dopamine beta-monooxygenase
Identifiers
EC no.	1.14.17.1
CAS no.	9013-38-1
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

The three substrates of the enzyme are dopamine, vitamin C (ascorbate), and O₂. The products are norepinephrine, dehydroascorbate, and H₂O.

DBH is a 290 kDa copper-containing oxygenase consisting of four identical subunits, and its activity requires ascorbate as a cofactor.^[5]

It is the only enzyme involved in the synthesis of small-molecule neurotransmitters that is membrane-bound, making norepinephrine the only known transmitter synthesized inside vesicles. It is expressed in noradrenergic neurons of the central nervous system (i.e. locus coeruleus) and peripheral nervous systems (i.e. sympathetic ganglia), as well as in chromaffin cells of the adrenal medulla.

Mechanism of catalysis

Based on the observations of what happens when there is no substrate, or oxygen, the following steps seem to constitute the hydroxylation reaction.^[6][7]

In the absence of oxygen, dopamine or other substrates, the enzyme and ascorbate mixture produces reduced enzyme and dehydroascorbate. Exposing the reduced enzyme to oxygen and dopamine results in oxidation of the enzyme and formation of noradrenaline and water, and this step doesn't require ascorbate.

Although details of DBH mechanism are yet to be confirmed, DBH is homologous to another enzyme, peptidylglycine α-hydroxylating monooxygenase (PHM). Because DBH and PHM share similar structures, it is possible to model DBH mechanism based on what is known about PHM mechanism.^[8]

Substrate specificity

Biosynthetic pathways for catecholamines and trace amines in the human brain[9][10][11] L-Phenylalanine L-Tyrosine L-DOPA Epinephrine Phenethylamine p-Tyramine Dopamine Norepinephrine N-Methylphenethylamine N-Methyltyramine p-Octopamine Synephrine 3-Methoxytyramine AADC AADC AADC primary pathway PNMT PNMT PNMT PNMT AAAH AAAH brain CYP2D6 minor pathway COMT DBH DBH In humans, catecholamines and phenethylaminergic trace amines are derived from the amino acid L-phenylalanine.

Dopamine beta-hydroxylase catalyzes the hydroxylation of not only dopamine but also other phenylethylamine derivatives when available. The minimum requirement seems to be the phenylethylamine skeleton: a benzene ring with a two-carbon side chain that terminates in an amino group.^[6]

Assays for DBH activity in human serum and cerebrospinal fluid

DBH activity in human serum could be estimated by a spectrophotometric method ^[12] or with the aid of Ultra high performance liquid chromatography with Photo Diode Array detector (UHPLC-PDA).^[13] A sensitive assay for the detection of DBH activity in cerebrospinal fluid using High-performance liquid chromatography with Electrochemical detector(HPLC-ECD) was also described earlier.^[14]

Expression quantitative trait loci (eQTLs) at DBH loci

Genetic variants such as single-nucleotide polymorphisms(SNPs)^[15][16] at DBH loci were found to be associated with DBH activity and are well known expression quantitative trait loci. Allele variants at two regulatory SNPs namely rs1611115 ^[17] and rs1989787 ^[18] were shown to affect transcription of this gene. Mutations identified in dopamine beta hydroxylase deficiency^[19] and non-synonymous SNPs such as rs6271 in this gene were found to cause defective secretion of the protein from the endoplasmic reticulum.^[20]

Clinical significance

DBH primarily contributes to catecholamine and trace amine biosynthesis. It also participates in the metabolism of xenobiotics related to these substances; for example, the human DBH enzyme catalyzes the beta-hydroxylation of amphetamine and para-hydroxyamphetamine, producing norephedrine and para-hydroxynorephedrine respectively.^[21][22][23]

DBH has been implicated as correlating factor in conditions associated with decision making and addictive drugs, e.g., alcoholism^[24] and smoking,^[25] attention deficit hyperactivity disorder,^[26] schizophrenia,^[27] and Alzheimer's disease.^[28] Inadequate DBH is called dopamine beta hydroxylase deficiency.

The proximal promoter SNPs rs1989787 and rs1611115 were found to be associated with cognition in schizophrenia subjects.^[29] Further these SNPs (rs1989787;rs1611115) and a distal promoter variant 19bp Ins/Del(rs141116007) were associated with scores of Abnormal Involuntary Movement Scale in tardive dyskinesia positive schizophrenia subjects.^[29] Of the three variants, the proximal promoter SNP(rs1611115) was associated with Positive and Negative Syndrome Scale(PANSS) scores in tardive dyskinesia positive schizophrenia subjects.^[29] The main effect of a putative splice variant in Dopamine beta-hydroxylase namely rs1108580 was found to be associated with Working memory _{Processing speed} in a north Indian Schizophrenia case control study where the G/G genotype of that single-nucleotide polymorphism(SNP) was found to have lower cognitive scores than those with A/A and A/G genotypes. Furthermore the same SNP was associated with Emotion _accuracy in healthy controls.^[30]

Structure

Experimental DBH structural model based upon in silico prediction and physiochemical validation^[31]

It was difficult to obtain a stable crystal of dopamine beta-hydroxylase. Hence an homology model based on the primary sequence and comparison to PHM is available.^[31]

However, a crystal structure was also put forward in 2016.^[32]

Regulation and inhibition

This protein may use the morpheein model of allosteric regulation.^[33]

Inhibitors

Types of dopamine beta-hydroxylase inhibition^{[clarification needed][citation needed]}

	HYD[a]	HP[b]	QCA[c]	IQCA[d]	BI[e]	IAA[f]
Competitive	Ascorbate	Ascorbate	Ascorbate	Ascorbate	Ascorbate	Ascorbate
Uncompetitive			Tyramine	Tyramine
Mixed	Tyramine	Tyramine			Tyramine	Tyramine
Ascorbate is cofactor; tyramine is substitute for dopamine, DBH's namesake substrate hydralazine 2-hydrazinopyridine 2-quinoline-carboxylic acid l-isoquinolinecarboxylic acid 2,2'-biimidazole imidazole-4-acetic acid

DBH is inhibited by disulfiram,^[34] tropolone,^[35] and, most selectively, by nepicastat.^[36] It is also inhibited by etamicastat and zamicastat.^[37]

DBH is reversibly inhibited by l-2H-Phthalazine hydrazone (hydralazine; HYD), 2-1H-pyridinone hydrazone (2-hydrazinopyridine; HP), 2-quinoline-carboxylic acid (QCA), l-isoquinolinecarboxylic acid (IQCA), 2,2'-bi-lH-imidazole (2,2'-biimidazole; BI), and IH-imidazole-4-acetic acid (imidazole-4-acetic acid; IAA). HYD, QCA, and IAA are allosteric competitive.^[38]

Nomenclature

The systematic name of this enzyme class is 3,4-dihydroxyphenethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating).

Other names in common use include:

• dopamine beta-monooxygenase
• dopamine beta-hydroxylase
• membrane-associated dopamine beta-monooxygenase (MDBH)
• soluble dopamine beta-monooxygenase (SDBH)
• dopamine-B-hydroxylase
• 3,4-dihydroxyphenethylamine beta-oxidase
• 4-(2-aminoethyl) pyrocatechol beta-oxidase
• dopa beta-hydroxylase
• dopamine beta-oxidase
• dopamine hydroxylase
• phenylamine beta-hydroxylase
• (3,4-dihydroxyphenethylamine) beta-mono-oxygenase