PMID: 6109756Jan 1, 1981Paper

The activity of rat pineal and brain tyrosine hydroxylase during the daily cycle of light and darkness as determined by the modified 14CO2 assay method

Journal of Neurochemistry
S WatanabeT Kataoka

Abstract

A previous published assay method for tyrosine hydroxylase by the evolution of 14CO2 was modified to a two-step procedure to allow reliable measurement of large numbers of samples containing low tyrosine hydroxylase activity. The reliability of the method was examined in detail. Properties of rat brain and pineal tyrosine hydroxylase solubilized with 0.2% Triton X-100 were as follows. The apparent Km values of the brain enzyme for L-tyrosine with 1 mM-(6-DL)-5,6,7,8-tetrahydro-L-erythro-biopterin (BPH4) as cofactor and for BPH4 with 62 microM-L-tyrosine as substrate were approximately 25 microM and 85 microM, respectively. The Km's for L-tyrosine with 1 mM-(6-DL)-5,6,7,8-tetrahydro-6-methylpterin (6MPH4) as cofactor and for 6MPH4 with 210 microM-L-tyrosine as substrate were 68 microM and 270 microM, respectively. The marked substrate inhibition by high concentrations of L-tyrosine was observed only when BPH4 was used as cofactor. High concentrations of BPH4 inhibited the reaction slightly. The kinetic properties of tyrosine hydroxylase in the pineal extract were similar to those of the brain enzyme, except that a Lineweaver-Burk plot of reciprocal velocity versus the reciprocal concentration of BPH4 with 62 microM-L-tyrosine as...Continue Reading

References

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Citations

Jan 1, 1982·Journal of Neural Transmission·M ToruM Takashima
Feb 13, 1997·Biochemical and Biophysical Research Communications·F FukamauchiM Kusakabe

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