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Endosome-lysosome fusion at low temperature
1Medical Biochemistry, University of Cape Town Medical School, Observatory, South Africa.
The Journal of Biological Chemistry
|May 5, 1991
Summary
Low temperature delays, but does not inhibit, endosome-lysosome fusion. This study reveals a pre-fusion step is affected, not the fusion process itself, impacting cellular trafficking research.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Low temperature is commonly used to inhibit endosome-lysosome fusion.
- The precise nature of this inhibition has not been fully characterized.
Purpose of the Study:
- To investigate the effect of low temperature on endosome-lysosome fusion.
- To characterize the kinetics and nature of low-temperature-induced inhibition of cellular trafficking.
Main Methods:
- Utilized covalent membrane markers (radioactive galactose-labeled glycoconjugates) and endocytic content markers (horseradish peroxidase, iodinated acetyl LDL) in mouse macrophage (P388D1) and human skin fibroblast cells.
- Analyzed membrane and content transfer to lysosomes via subcellular fractionation at 16°C over extended periods.
- Investigated the effect of pre-incubation at 37°C followed by cooling to 16°C on fusion kinetics.
Main Results:
- Significant transfer of both membrane and content markers to high-density lysosomes was observed even at 16°C over 24 hours.
- Transfer to lysosomes showed a lag phase of approximately 6 hours at 16°C.
- Initiating transfer at 37°C and then cooling to 16°C did not halt the ongoing transfer, which proceeded with similar kinetics.
Conclusions:
- Low temperature does not inhibit endosome-lysosome fusion directly.
- Low temperature imposes a delay on an unidentified step preceding fusion.
- This finding clarifies the mechanism of low-temperature effects on cellular membrane trafficking.