Localization of NADP-dependent isocitrate dehydrogenase in rat kidney peroxisomes

The localization of NADP-dependent isocitrate dehydrogenase (cytosolic type, ICD2) in rat kidney peroxisomes was studied using an immunoelectron microscopic technique. Rat kidneys were perfusion-fixed in a fixative consisting of 4% paraformaldehyde, 0.2% glutaraidehyde and 0.1 M Hepes-KOH buffer (pH 7.4) for 10 min. Fixed tissue slices were embedded in LR White resin. Thin sections were stained for ICD2 with a combination of anti-ICD2 and protein A-gold probe (15 nm). Signals for ICD2 were found to be present in the peroxisomes of the proximal tubules but not in the cytoplasmic matrix. Within the peroxisomes, ICD2 was detected in the peripheral dense matrix where catalase was present but not in the central clear matrix to which D-amino acid oxidase was confined. The results showed that in the rat kidney ICD2 was confined to the peroxisomes and located in the peripheral dense matrix as catalase.