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The rate of Cu,Zn superoxide dismutase evolution
J Kwiatowski1, R R Hudson, F J Ayala
1Department of Ecology and Evolutionary Biology, University of California, Irvine 92717.
Free Radical Research Communications
|January 1, 1991
Summary
The molecular clock
Area of Science:
- Biochemistry
- Evolutionary Biology
- Molecular Evolution
Background:
- Copper-zinc superoxide dismutase (Cu,Zn SOD) is a crucial antioxidant enzyme.
- The molecular clock hypothesis predicts constant rates of amino acid substitution.
- Observed amino acid replacement rates in Cu,Zn SOD deviate significantly from molecular clock predictions.
Purpose of the Study:
- To investigate the evolutionary rate and patterns of Cu,Zn SOD across diverse species.
- To reconcile the observed evolutionary rates with molecular clock expectations.
- To explore mathematical models describing the declining rate of Cu,Zn SOD evolution.
Main Methods:
- Comparative analysis of 27 Cu,Zn SOD amino acid sequences.
- Examination of evolutionary divergence across mammalian families, plants, fungi, and prokaryotes.
- Statistical analysis of amino acid replacement rates and comparison with Poisson processes.
Main Results:
- Cu,Zn SOD evolution shows a consistent decline in replacement rates over time across lineages.
- Mammalian Cu,Zn SOD evolution suggests a simultaneous radiation event.
- Plant chloroplast Cu,Zn SODs exhibit less divergence than cytoplasmic forms.
- Bacteriocuprein, fluke, and human extracellular SOD are highly divergent.
Conclusions:
- The molecular clock is not uniformly applicable to Cu,Zn SOD evolution.
- Cu,Zn SOD evolution is influenced by lineage-specific factors and a general rate decline.
- Mathematical models can describe the observed decrease in evolutionary rates.
- Findings may inform models for other proteins with disparate evolutionary rates.