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Dopamine-4-O-sulfate: a possible precursor of free norepinephrine
Canadian Journal of Biochemistry
|September 1, 1979
Summary
Dopamine-4-O-sulfate is converted to norepinephrine by dopamine-beta-hydroxylase. This reaction, inhibited by fusaric acid, follows Michaelis-Menten kinetics, indicating a direct enzymatic conversion.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Dopamine metabolism is crucial for neurotransmission.
- Dopamine-4-O-sulfate is a metabolite of dopamine.
- Dopamine-beta-hydroxylase (DBH) is the enzyme responsible for converting dopamine to norepinephrine.
Purpose of the Study:
- To investigate the enzymatic conversion of dopamine-4-O-sulfate to norepinephrine.
- To determine the kinetic parameters of this reaction.
- To assess the role of dopamine-beta-hydroxylase in this process.
Main Methods:
- Incubation of dopamine-4-O-sulfate with purified bovine dopamine-beta-hydroxylase.
- Assay for norepinephrine formation.
- Inhibition studies using fusaric acid.
- Kinetic analysis using Michaelis-Menten model.
Main Results:
- Dopamine-4-O-sulfate was converted to free norepinephrine by dopamine-beta-hydroxylase.
- Fusaric acid completely inhibited norepinephrine production.
- No significant sulfatase activity was detected.
- The reaction followed Michaelis-Menten kinetics with an apparent Km of 2.6 mM.
Conclusions:
- Dopamine-beta-hydroxylase directly converts dopamine-4-O-sulfate to norepinephrine.
- This enzymatic pathway is sensitive to dopamine-beta-hydroxylase inhibitors.
- The kinetic data suggest a specific interaction between the enzyme and its substrate.