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The tyrosine hydroxylase activity of mammalian tyrosinase

, : The tyrosine hydroxylase activity of mammalian tyrosinase. Journal of Biological Chemistry 241(1): 161-168

The tyrosine hydroxylase activity of tyrosinase from hamster melanoma has been studied by measurement of the release of tritium from tyrosine-3, 5-h3. Experiments with mixtures of tyrosine-3, 5-H3 and tyrosine-C14 show that there is little or no tritium rate effect in this reaction. DOPA (dihydroxyphenylalanine) is the most effective hydrogen donor and will eliminate the lag period when used in catalytic amounts. 2-Amino-6, 7-dimethyl-4-hydroxy-5, 6, 7,8-tetrahydropteri-dine eliminates the lag when it is at a concentration of 2.4x10-3 [image] and shortens the lag at lower concentrations. Substrate quantities of ascorbate, TPNA (reduced triphosphopyridine nucleotide), DPNH (reduced dyshosphopyridine nucleotide), dopamine, epinephrine, and norepinephrine do not abolish the lag. DOPA at high concentration is an inhibitor of tyrosine hydroxylation, while tyrosine acts as a substrate inhibitor at concentrations above 8x10-4 [image]. The substrate inhibition can be partially reversed by increasing the concentration of DOPA from the catalytic level to 8x10-4 [image]. Ascorbate magnifies the inhibition by DOPA. Inhibition by cyanide, diethyldithiocarbamate, 5-hydroxyindole and 5-hydroxy-DL-tryptophan is also reported.


PMID: 5294951

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