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Peroxisomes: identification in freeze-etch preparations of rat kidney
Abstract:
The definitive identification of peroxisomes in freeze-etch preparations of normal mammalian cells has been impeded due to their similarity to other globular cytoplasmic organelles, especially the lysosomes. In the proximal tubules of the rat kidney there is a distinct group of large microbodies with an angular shape and crystalline inclusions which have now been identified in freeze-etch replicas. Rat kidneys were fixed by perfusion with glutaradehyde and processed for catalase cytochemistry and freeze-etching. In ultrathin sections catalase positive peroxisomes 0.5-2 microns in diameter with an angular multifaceted shape and scalloped margins were found. In freeze-etch replicas particles with the same size, shape, and intracellular distribution were found; these contained branching and anastomosing tubular inclusions. The tubules, 100-125 nm in diameter, left deep impressions upon the limiting membrane of peroxisomes. A crystalline pattern with a periodicity of approximately 92 +/- 8 A perpendicular to the axis of the tubles was noted on the E-face of the microbody membrane. In addition, a few membrane particles were present on the E-face, but many more particles were noted on the P-face of the microbody membrane. The cisternae of ER, with typical fenestrations, wrapped around large portions of the surface of peroxisomes, thus demonstrating the close association of these two organelles.
Insights
Freeze-etching successfully identified peroxisomes in rat kidney proximal tubules, distinguishing them from lysosomes. These peroxisomes exhibit unique angular shapes and crystalline inclusions, aiding in their definitive identification.
Area of Science:
- Cell Biology
- Microscopy
- Organelle Identification
Background:
- Peroxisome identification in freeze-etch preparations is challenging due to similarity with other organelles like lysosomes.
- Rat kidney proximal tubules contain distinct large microbodies with angular shapes and crystalline inclusions.
Purpose of the Study:
- To definitively identify peroxisomes in freeze-etch replicas of rat kidney proximal tubules.
- To characterize the ultrastructural features of these peroxisomes using freeze-etching and cytochemistry.
Main Methods:
- Rat kidneys were fixed via glutaraldehyde perfusion.
- Catalase cytochemistry and freeze-etching techniques were employed.
- Ultrathin sectioning and freeze-etch replica analysis were performed.
Main Results:
- Catalase-positive peroxisomes (0.5-2 microns) showed angular, multifaceted shapes with scalloped margins in ultrathin sections.
- Freeze-etch replicas revealed similar-sized particles with angular shapes and crystalline, tubular inclusions.
- Peroxisome membranes displayed crystalline patterns and differential particle distribution on E-face and P-face.
- Endoplasmic reticulum cisternae were observed closely associated with peroxisomes.
Conclusions:
- Freeze-etching, combined with cytochemistry, provides definitive identification of rat kidney peroxisomes.
- Distinct morphological features, including crystalline inclusions and membrane characteristics, differentiate these peroxisomes.
- The close association between endoplasmic reticulum and peroxisomes is highlighted.