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Intramembranous particles are clustered on microvillus membrane vesicles
Abstract:
Many intramembranous particles in pig jejunal microvillus membranes cluster during cell disruption and membrane vesiculation with the MgCl2 aggregation technique (Hauser, H., Howell, K., Dawson, R.M.C. and Bowyer, D.E. (1980) Biochim. Biophys. Acta 602, 567-577). Isolated brush borders and purified microvillus membrane vesicles were jet-frozen and examined by freeze-fracture electron microscopy. From 30 to 60% of purified vesicles exhibited no intramembranous particles on their fracture face and 22-39% exhibited clustered or aggregated intramembranous particles. Only 6-15% of the vesicles exhibited the random distribution of intramembranous particles that is characteristic of intact enterocytes. Aggregation was not reversed after dialysis to remove divalent cations. Prior freezing of tissue or vesicles (-70 degrees C) gave the same results as fresh unfrozen material. Heterogeneity of microvillus vesicles may occur among the vesicles generated from a single microvillus.
Insights
Intramembranous particles in pig jejunal microvillus membranes aggregate during cell disruption. This particle aggregation, observed in purified vesicles, was not reversed by dialysis or freezing.
Area of Science:
- Cell Biology
- Biochemistry
- Membrane Biology
Background:
- Microvillus membranes are crucial for nutrient absorption in the jejunum.
- Intramembranous particles represent proteins embedded within these membranes.
- Understanding their distribution is key to membrane function.
Purpose of the Study:
- To investigate the distribution of intramembranous particles in pig jejunal microvillus membranes.
- To assess the impact of cell disruption and membrane vesiculation on particle arrangement.
- To determine if particle aggregation is reversible.
Main Methods:
- Isolation of brush borders and purification of microvillus membrane vesicles.
- Jet-freezing of samples for preservation.
- Freeze-fracture electron microscopy for visualizing membrane structures.
Main Results:
- 30-60% of purified vesicles lacked intramembranous particles.
- 22-39% of vesicles showed clustered or aggregated particles.
- Only 6-15% of vesicles displayed the random particle distribution seen in intact cells.
- Aggregation persisted after dialysis and was unaffected by prior freezing.
Conclusions:
- Cell disruption and MgCl2 aggregation technique cause significant intramembranous particle clustering in pig jejunal microvillus vesicles.
- The observed aggregation is largely irreversible under tested conditions.
- Significant heterogeneity in vesicle composition may arise during microvillus preparation.