Tyrosine hydroxylase is a BH4 (tetrahydrobiopterin) dependent enzyme which increases the conversion of tyrosine, an amino acid, to l-DOPA (l-dihydroxyphenylalanine.) This enzyme activity was measured in multiple parts of the leguminous plant, Mucuna pruriens (velvet bean.) l-DOPA is a treatment for Parkinsonism. It crosses the blood-brain barrier and is converted to dopamine in the brain.
In Parkinsonism, the substantia nigra area of the brain doesn’t produce enough dopamine. Parkinson’s disease is a neurodegenerative disease. Tyrosine hydroxylase enzyme promotes the conversion of tyramine to dopamine. These two processes are necessary in the production of dopamine from tyrosine.
The immature seeds of Mucuna pruriens (velvet bean) were found to contain the highest amounts of l-DOPA. The roots and stems had the lowest. The young leaves of the plant contained the highest amounts of tyrosine hydroxylase. The immature seeds had the lowest amount of tyrosine hydroxylase. The enzyme levels in mature leaves were the highest and the levels in old leaves were the lowest.
Phenylalanine could not be hydroxylated by the tyrosine hydroxylase from Macuna pruriens. The activity of tyrosine hydroxylase was enhanced by low levels of iron and was inhibited by high levels of iron.
CONCLUSION: High levels of tyrosine hydroxylase are found in Mucuna pruriens plants. This enzyme is important in the production of l-DOPA and dopamine in the brain for treatment of Parkinsonism.
NOTE: Insufficient BH4 can inhibit the reactions necessary for the production of serotonin and dopamine.
The hairs of M. pruriens contain serotonin (5-OH tryptophan.)
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PMID: 20300771.
Summary #378.
