Immunocytochemical localization of L-alpha-hydroxyacid oxidase in dense bar of dumb-bell-shaped peroxisomes of monkey kidney

Be different--the diversity of peroxisomes in the animal kingdom

Peroxisomes represent so-called "multipurpose organelles" as they contribute to various anabolic as well as catabolic pathways. Thus, with respect to the physiological specialization of an individual organ or animal species, peroxisomes exhibit a functional diversity, which is documented by significant variations in their proteome. These differences are usually regarded as an adaptational response to the nutritional and environmental life conditions of a specific organism. Thus, human peroxisomes can be regarded as an in part physiologically unique organellar entity fulfilling metabolic functions that differ from our animal model systems. In line with this, a profound understanding on how peroxisomes acquired functional heterogeneity in terms of an evolutionary and mechanistic background is required. This review summarizes our current knowledge on the heterogeneity of peroxisomal physiology, providing insights into the genetic and cell biological mechanisms, which lead to the differential localization or expression of peroxisomal proteins and further gives an overview on peroxisomal biochemical pathways, which are specialized in different animal species and organs. Moreover, it addresses the impact of proteome studies on our understanding of differential peroxisome function describing the utility of mass spectrometry and computer-assisted algorithms to identify peroxisomal target sequences for the detection of new organ- or species-specific peroxisomal proteins.

Localization of cytosolic NADP-dependent isocitrate dehydrogenase in the peroxisomes of rat liver cells: biochemical and immunocytochemical studies

Two types of NADP-dependent isocitrate dehydrogenases (ICDs) have been reported: mitochondrial (ICD1) and cytosolic (ICD2). The C-terminal amino acid sequence of ICD2 has a tripeptide peroxisome targeting signal 1 sequence (PTS1). After differential centrifugation of the postnuclear fraction of rat liver homogenate, approximately 75% of ICD activity was found in the cytosolic fraction. To elucidate the true localization of ICD2 in rat hepatocytes, we analyzed the distribution of ICD activity and immunoreactivity in fractions isolated by Nycodenz gradient centrifugation and immunocytochemical localization of ICD2 antigenic sites in the cells. On Nycodenz gradient centrifugation of the light mitochondrial fraction, ICD2 activity was distributed in the fractions in which activity of catalase, a peroxisomal marker, was also detected, but a low level of activity was also detected in the fractions containing activity for succinate cytochrome C reductase (a mitochondrial marker) and acid phosphatase (a lysosomal marker). We have purified ICD2 from rat liver homogenate and raised a specific antibody to the enzyme. On SDS-PAGE, a single band with a molecular mass of 47 kD was observed, and on immunoblotting analysis of rat liver homogenate a single signal was detected. Double staining of catalase and ICD2 in rat liver revealed co-localization of both enzymes in the same cytoplasmic granules. Immunoelectron microscopy revealed gold particles with antigenic sites of ICD2 present mainly in peroxisomes. The results clearly indicated that ICD2 is a peroxisomal enzyme in rat hepatocytes. ICD2 has been regarded as a cytosolic enzyme, probably because the enzyme easily leaks out of peroxisomes during homogenization. (J Histochem Cytochem 49:1123-1131, 2001)