Studies on peroxisomes: I. Intraparticulate localization of peroxisomal enzymes in rat liver

Abstract

Particles containing catalase, d-amino acid oxidase, urate oxidase and l-α-hydroxy acid oxidase were isolated from rat liver homogenate and were treated with Triton X-100, repeated freezing-thawing and heat-treated habu venom. After density gradient centrifugation the enzyme activities were determined. Catalase was most easily solubilized from the particles with these treatments, while urate oxidase was not solubilized. Urate oxidase migrated to the fraction of density 1.27 or more after the particles had been treated with Triton X-100, despite the fact that the intact peroxisomes were found in the density fraction 1.23–1.25. These results support the view of C. De Duve and P. Baudhuin ( Physiol. Rev., 46 (1966) 323) that catalase exists in the matrix of the peroxisomes and urate oxidase in the core. About half of the d-amino acid oxidase activity was solubilized with Triton X-100 and the activity remaining in the particles was found in the fraction of density 1.27 or more. The latter activity was completely solubilized with heat-treated habu venom. The behavior of l-α-hydroxy acid oxidase under those conditions showed a similarity to that of d-amino acid oxidase. From these results, it was found that tightness of binding of the four enzymes studied to heavy sedimentable material (“core”) increased in the order: catalase, l-α-hydroxy acid oxidase, d-amino acid oxidase, urate oxidase.