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Microsomal cytochrome P-450: substrate binding, membrane interactions, and topology.
G Vergères1, K H Winterhalter, C Richter
1Laboratory of Biochemistry, Swiss Federal Institute of Technology, Zürich, Switzerland.
Mutation Research
|July 1, 1989
Summary
The microsomal monoxygenase system, featuring cytochrome P-450, metabolizes compounds. New evidence suggests cytochrome P-450 spans the membrane with a single segment, with most of its mass in the cytosol.
Area of Science:
- Biochemistry
- Molecular Biology
- Cellular Biology
Background:
- The microsomal monoxygenase system is crucial for metabolizing endogenous substances and xenobiotics.
- This system detoxifies compounds but can also activate procarcinogens into carcinogens.
- Cytochrome P-450 is the key terminal enzyme within this system.
Purpose of the Study:
- To review current understanding of cytochrome P-450.
- To investigate the enzyme's active site, membrane interactions, and membrane topology.
- To present new evidence regarding cytochrome P-450's membrane integration.
Main Methods:
- Review of existing literature on cytochrome P-450.
- Analysis of tryptophan fluorescence data.
- Membrane protein topology studies.
Main Results:
- Strong evidence indicates cytochrome P-450 spans the membrane via a single, short segment.
- Tryptophan fluorescence analysis supports that the majority of the protein resides in the cytosolic space.
- This finding contrasts with previous models of cytochrome P-450 membrane topology.
Conclusions:
- Cytochrome P-450's membrane topology is characterized by a single transmembrane segment.
- Most of the cytochrome P-450 protein mass is accessible to the cytosol.
- This structural understanding is vital for comprehending its metabolic functions.