Biogenesis of peroxisomes in regenerating rat liver. I. Sequential changes of catalase and urate oxidase detected by ultrastructural cytochemistry.

The biogenesis of peroxisomes has been investigated in the model of regenerating rat liver after partial hepatectomy using ultrastructural cytochemical staining methods: catalase as a marker of the peroxisomal matrix and uricase for the cores. The peroxisomes in regenerating rat liver showed several distinctive features: a) marked variation in shape and size, e.g., peroxisomes with tail-like extensions and tortuously elongated rod-shaped ones, b) formation of peroxisomal clusters and, c) interconnections between adjacent peroxisomes suggesting cleavage or budding. Whereas the reaction product for catalase was present at all intervals after hepatectomy in the matrix of all peroxisomes, the pattern of localization of uricase case varied with the time. It was confined to the cores in controls and at 10 days after the operation, while at 24 and 48 h it showed, in addition, a diffuse reaction in the matrix of some peroxisomes. In interconnected apparently dividing peroxisomes, the core with positive uricase reaction was present only in one half, while the other half was devoid of the reaction product. Similarly, the diffuse uricase staining was confined to the half which contained the core with the other half remaining unstained. These observations are consistent with the concept that new peroxisomes are formed from preexisting ones by budding and segmentation. While catalase is transferred uniformly to all new segments, uricase is compartmentalized in certain portions, of the apparently growing "peroxisomal reticulum".