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Membrane structure: spin labeling and freeze etching of Mycoplasma laidawii
Abstract:
A spin-labeled fatty acid was incorporated in vivo into the polar lipids of Mycoplasma laidlawii membranes. The electron paramagnetic resonance signal from either intact cells or their extracted lipids reflected the fatty acid composition of the Mycoplasma membranes. Comparison of signals from intact cells, gramicidin-treated cells, heat-treated cells, and extracted lipids indicates that a major portion of the membrane lipids is in a semiviscous hydrocarbon environment. The results also show that the spin label in the intact membrane is slightly but significantly less mobile than it is in protein-free lipid extracts made from these membranes. Correlated electron microscope examinations using the freeze-etch technique reveal particulate components in the hydrophobic region of the membrane. The mobility of the lipids in the intact cell membrane may be influenced by their association with these particles.
Insights
Spin-labeled fatty acids reveal Mycoplasma laidlawii membrane lipid environments. Membrane lipids exist in a semiviscous state, with mobility influenced by associated membrane particles.
Area of Science:
- Biochemistry
- Membrane Biology
- Microbiology
Background:
- Mycoplasma laidlawii possesses a cell membrane lacking a cell wall.
- Understanding the physical state and dynamics of membrane lipids is crucial for cell function.
Purpose of the Study:
- To investigate the physical state and mobility of lipids within the Mycoplasma laidlawii cell membrane.
- To determine if membrane proteins influence lipid mobility.
Main Methods:
- Incorporation of spin-labeled fatty acids into Mycoplasma laidlawii polar lipids in vivo.
- Electron paramagnetic resonance (EPR) spectroscopy of intact cells, treated cells, and extracted lipids.
- Freeze-etch electron microscopy to visualize membrane structure.
Main Results:
- EPR signals confirmed the fatty acid composition of Mycoplasma membranes.
- A significant portion of membrane lipids resides in a semiviscous hydrocarbon environment.
- Lipid mobility in intact membranes was slightly but significantly reduced compared to protein-free lipid extracts.
- Electron microscopy revealed particulate components in the membrane's hydrophobic region.
Conclusions:
- The Mycoplasma laidlawii membrane lipids exist in a semiviscous state.
- The mobility of membrane lipids is influenced by their association with membrane structural components, likely proteins.