Extraction and purification of yellow-fluorescent lipofuscin in rat kidney

Yellow fluorescent lipofuscin deposited in rat tissues was extracted in an aqueous solution. Yellow fluorescence with fluorescence maxima at 400/615-620 nm was detected in the aqueous extracts of brain and kidney of older rats. Purification and characterization of the yellow fluorescent components extracted from rat kidney were attempted. Centrifugal fractionation of the extract revealed that the flourescence was detected in the 105,000 g supernatant, and not in nuclei, mitochondria, lysosomes, microsomes and cell debris. Gel filtration of the supernatant through Sephadex columns gave at least 5 yellow fluorescent components with different molecular weights. The higher-molecular-weight components were converted into the smaller ones on treatment with alkali or ethanol, but may not be on protease treatment. These components were adherent to polymers composed of sugars. They were soluble in water and not in an organic solvent. While the yellow fluorophores were stable on borohydride treatment, they were destroyed on heavy metal ion treatment. The characteristics of the yellow fluorophores were different from those of bluish lipofuscin-like fluorophores generated by lipid peroxidation.