Immunocytochemical localization of Δ³, Δ²-enoyl-CoA isomerase and NADPH-dependent-2,4-dienoyl-CoA reductase in rat kidney

Localization of Δ³, Δ²-enoyl-CoA isomerase (ECI) and NADPH-dependent-2,4-dienoyl-CoA reductase (DCR) in the rat kidney was investigated by immunocytochemical techniques. The kidneys were perfusion-fixed and embedded in Epon or LR White. For light microscopy, semi-thin sections of Epon-embedded materials were stained by the immunoenzyme technique after the epoxy resin was removed by treatment with sodium ethoxide. For electron microscopy, ultra-thin sections of LR White-embedded materials were stained by the protein A-gold technique. By light microscopy, the S1 segment of the proximal tubule was most heavily stained for ECI and DCR whilst S2 and S3 segments showed intermediate staining. A weak staining reaction was observed in the distal tubule and the medullary collecting tubule. In the cortical collecting tubule, heavily stained cells were present between weakly stained cells. By electron microscopy, gold particles showing the antigenic sites for ECI were confined mainly to the mitochondria, but few particles were observed in the peroxisomes. Gold labeling for DCR was localized both in the mitochondria and the peroxisomes. The labeling intensity of the peroxisomes was much higher than that of the mitochondria. The results suggest that metabolism of unsaturated fatty acids occurs mainly in the mitochondria and the peroxisomes of the proximal tubule in the kidney.