Related Experiment Videos
The free radical in ribonucleotide reductase from E. coli
Ciba Foundation Symposium
|January 1, 1977
Summary
The study reveals that Protein B2 of Escherichia coli ribonucleotide reductase has a stable free radical on a tyrosyl residue, stabilized by iron atoms. This radical is likely crucial for the enzyme's active site function.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Ribonucleotide reductase (RR) is essential for DNA synthesis.
- Escherichia coli RR consists of two subunits: B1 and B2.
- Protein B2 is known to contain a stable free radical.
Purpose of the Study:
- To characterize the free radical in Protein B2.
- To elucidate the role of iron atoms in stabilizing the radical.
- To understand the structural and functional relationship between subunits B1 and B2.
Main Methods:
- Electron paramagnetic resonance (EPR) spectroscopy to detect and characterize the free radical.
- Optical spectroscopy to analyze spectral properties.
- Biochemical analysis of protein subunits and their interactions.
Main Results:
- Protein B2 exhibits a characteristic EPR doublet signal and an optical absorption peak at 410 nm.
- The free radical is localized on a tyrosyl residue with delocalized spin density.
- Two antiferromagnetically-coupled iron(III) atoms in Protein B2 stabilize the tyrosyl radical.
- Protein B1 contains substrate and allosteric effector binding sites.
- The active enzyme is a B1-B2 complex, with the radical likely at the active site.
Conclusions:
- The tyrosyl radical in Protein B2 is a key component of the ribonucleotide reductase active site.
- Iron cofactors play a critical role in maintaining the stability of the radical.
- The interaction between B1 and B2 subunits is essential for enzymatic activity.