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Lag kinetics of tyrosinase: its physiological implications
1Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.
Indian Journal of Biochemistry & Biophysics
|October 1, 1996
Summary
The lag kinetics of tyrosinase enzyme activity, crucial for melanin production, are not explained by tyrosine competition. An allosteric enzyme model remains a plausible explanation for this conserved enzymatic behavior.
Area of Science:
- Biochemistry
- Enzymology
- Melanin Biosynthesis
Background:
- Tyrosinase is a key enzyme in melanin biosynthesis.
- The enzyme exhibits characteristic lag kinetics during L-tyrosine oxidation.
- Understanding these kinetics is vital for comprehending melanin production regulation.
Purpose of the Study:
- To review and evaluate existing theories explaining tyrosinase lag kinetics.
- To assess the validity of hypotheses involving tyrosine and dopa competition.
- To explore alternative explanations for the observed enzymatic behavior.
Main Methods:
- Literature review of tyrosinase kinetics theories.
- Analysis of experimental data from the author's laboratory.
- Comparison of hypotheses with existing biochemical evidence.
Main Results:
- The hypothesis of tyrosine and dopa competition for met-tyrosinase, forming a dead-end complex, is inconsistent with available data.
- The proposed allosteric enzyme model, where tyrosine acts as a negative effector and dopa competes for this site, is not disproved.
- The conserved lag kinetics of tyrosinase may have a physiological role.
Conclusions:
- The precise mechanism for tyrosinase lag kinetics requires further investigation.
- An allosteric model for tyrosinase remains a viable explanation.
- Lag kinetics may function to maintain enzyme inactivity during melanosome transport, with activation occurring at acidic pH within the organelle.