Peroxisomes: identification in freeze-etch preparations of rat kidney.

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.