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Assays for mammalian tyrosinase: a comparative study.
J R Jara1, F Solano, J A Lozano
1Departamento de Bioquímica, Facultad de Medicina, Universidad de Murcia, Spain.
Pigment Cell Research
|January 1, 1988
Summary
This study compared three tyrosinase activity assays. Mammalian tyrosinase shows higher activity with L-dopa than L-tyrosine, with proposed conversion factors for accurate enzyme measurement.
Area of Science:
- Biochemistry
- Enzymology
- Melanogenesis research
Background:
- Tyrosinase is a key enzyme in melanin production.
- Standard assays for tyrosinase activity include radiometric and spectrophotometric methods.
- Understanding assay correlations is crucial for accurate enzyme characterization.
Purpose of the Study:
- To compare three common tyrosinase activity assays.
- To investigate correlations between assays across different isozymes and purification levels.
- To establish conversion factors for inter-assay comparisons.
Main Methods:
- Comparative analysis of two radiometric assays (tyrosine hydroxylase, melanin formation) and one spectrophotometric assay (dopa oxidase).
- Simultaneous measurement of soluble, melanosomal, and microsomal tyrosinase isozymes from Harding-Passey mouse melanoma.
- Purification process monitoring of tyrosinase isozymes.
Main Results:
- Mammalian tyrosinase exhibits a higher turnover rate for L-dopa compared to L-tyrosine.
- Enzyme activity measurements are higher using L-dopa as a substrate.
- Melanin formation assay results are influenced by factors reducing apparent tyrosinase activity.
Conclusions:
- Proposed average inter-assay conversion factors: 10 (melanin formation to tyrosine hydroxylase), 100 (tyrosine hydroxylase to dopa oxidase), and 1,000 (melanin formation to dopa oxidase).
- Assay correlations can be affected by inhibitors or regulatory factors in melanogenesis.
- These findings aid in standardizing tyrosinase activity measurements.