Dopamine beta-hydroxylase (DBH), also known as dopamine beta-monooxygenase, is an enzyme (EC1.14.17.1) that in humans is encoded by the DBH gene. Dopamine beta-hydroxylase catalyzes the conversion of dopamine to norepinephrine.
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]
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]
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
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
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]
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^Punchaichira TJ, Deshpande SN, Thelma BK (2018). "Determination of Dopamine-β-hydroxylase Activity in Human Serum Using UHPLC-PDA Detection". Neurochemical Research. 43 (12): 2324–2332. doi:10.1007/s11064-018-2653-1. PMID30357655. S2CID53024826.
^Matsui H, Kato T, Yamamoto C, Fujita K, Nagatsu T (1981). "Highly sensitive assay for dopamine-beta-hydroxylase activity in human cerebrospinal fluid by high performance liquid chromatography-electrochemical detection: properties of the enzyme". Journal of Neurochemistry. 37 (2): 289–296. doi:10.1111/j.1471-4159.1981.tb00454.x. PMID7264660. S2CID42736106.
^Punchaichira TJ, Prasad S, Deshpande SN, Thelma BK (2016). "Deep sequencing identifies novel regulatory variants in the distal promoter region of the dopamine-beta-hydroxylase gene". Pharmacogenetics and Genomics. 26 (7): 311–23. doi:10.1097/FPC.0000000000000214. PMID26959714. S2CID205601803.
^Punchaichira TJ, Dey SK, Mukhopadhyay A, Kundu S, Thelma BK (2017). "Characterization of SNPs in the dopamine-beta-hydroxylase gene providing new insights into its structure-function relationship". Neurogenetics. 18 (3): 155–168. doi:10.1007/s10048-017-0519-3. PMID28707163. S2CID5259134.
^Glennon RA (2013). "Phenylisopropylamine stimulants: amphetamine-related agents". In Lemke TL, Williams DA, Roche VF, Zito W (eds.). Foye's principles of medicinal chemistry (7th ed.). Philadelphia, US: Wolters Kluwer Health/Lippincott Williams & Wilkins. pp. 646–648. ISBN9781609133450. Archived from the original on 8 March 2024. Retrieved 11 September 2015. The phase 1 metabolism of amphetamine analogs is catalyzed by two systems: cytochrome P450 and flavin monooxygenase. ... Amphetamine can also undergo aromatic hydroxylation to p-hydroxyamphetamine. ... Subsequent oxidation at the benzylic position by DA β-hydroxylase affords p-hydroxynorephedrine. Alternatively, direct oxidation of amphetamine by DA β-hydroxylase can afford norephedrine.
^Mutschler J, Abbruzzese E, Witt SH, Dirican G, Nieratschker V, Frank J, Grosshans M, Rietschel M, Kiefer F (August 2012). "Functional polymorphism of the dopamine β-hydroxylase gene is associated with increased risk of disulfiram-induced adverse effects in alcohol-dependent patients". Journal of Clinical Psychopharmacology. 32 (4): 578–80. doi:10.1097/jcp.0b013e31825ddbe6. PMID22760354.
^Bhaduri N, Sinha S, Chattopadhyay A, Gangopadhyay PK, Singh M, Mukhopadhyay KK (February 2005). "Analysis of polymorphisms in the dopamine beta hydroxylase gene: association with attention deficit hyperactivity disorder in Indian children". Indian Pediatrics. 42 (2): 123–9. PMID15767706.
^Punchaichira TJ, Kukshal P, Bhatia T, Deshpande SN (2023). "Effect of rs1108580 of DBH and rs1006737 of CACNA1C on Cognition and Tardive Dyskinesia in a North Indian Schizophrenia Cohort". Molecular Neurobiology. 60 (12): 6826–6839. doi:10.1007/s12035-023-03496-4. PMID37493923. S2CID260162784.
^Goldstein M, Anagnoste B, Lauber E, Mckeregham MR (July 1964). "Inhibition of dopamine- β -hydroxylase by disulfiram". Life Sciences. 3 (7): 763–7. doi:10.1016/0024-3205(64)90031-1. PMID14203977.
^Goldstein M, Lauber E, Mckereghan MR (July 1964). "The inhibitionof dopamine-β-hydroxylase by tropolone and other chelating agents". Biochemical Pharmacology. 13 (7): 1103–6. doi:10.1016/0006-2952(64)90109-1. PMID14201135.
^Dey SK, Saini M, Prabhakar P, Kundu S (September 2020). "Dopamine β hydroxylase as a potential drug target to combat hypertension". Expert Opin Investig Drugs. 29 (9): 1043–1057. doi:10.1080/13543784.2020.1795830. PMID32658551.
^Townes S, Titone C, Rosenberg RC (February 1990). "Inhibition of dopamine beta-hydroxylase by bidentate chelating agents". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1037 (2): 240–7. doi:10.1016/0167-4838(90)90174-E. PMID2306475.