STUDIES ON MICROPEROXISOMES III. OBSERVATIONS ON HUMAN AND RAT HEPATOCYTES

Normal human and rat liver, unincubated or following incubation in a 3,3'-diaminobenzidine (DAB), pH 9.7, procedure which visualizes catalase-containing peroxisomes, were studied by electron microscopy. In human hepatocytes the DAB-positive organelles are microperoxisomes, i.e., anucleoid cytoplasmic organelles characterized by numerous slender communications with smooth endoplasmic reticulum (ER) and a moderately electron-opaque matrix. These connections are best seen by viewing the specimen at different tilt angles. Rat hepatocytes possess both DAB-positive anucleoid (verified by serial sectioning) microperoxisomes and DAB-positive nucleoid-containing peroxisomes. The numerous slender connections with smooth ER are present in both. The peroxisomes may also possess wide type continuities with the ER. The significance of smooth ER cisternae adjacent to peroxisomes, noted by numerous electron microscopists, is clarified by the frequent finding of slender communications between these two organelles. A possible sequence of development of microperoxisomes into peroxisomes in rat liver is presented. Close spatial relations to lipid droplets of three organelles—ER, mitochondria and microperoxisomes—are described.