Peroxisomes in the liver of frog, Bombina orientalis.

The existence of peroxisomes was investigated in the liver of frog, Bombina orientalis, which characteristically cannot degrade cholesterol further than to C27 higher bile acids such as 3α, 7α, 12α-trihydroxy-5β-cholestanoic acid (THCA) or 3α, 7α-dihydroxy-5β-cholestanoic acid (DHCA). The activities of catalase, D-amino acid oxidase, urate oxidase, and the CN-insensitive fatty acyl-CoA β-oxidizing system (FAOS) were used as markers of peroxisomes. Catalase activity was present to almost the same extent in Bombina liver as in rat liver. D-Amino acid oxidase and urate oxidase were also present in the frog liver, but the activities were much lower than those in the rat liver. In a cell fractionation experiment, the highest specific activities of catalase, D-amino acid oxidase, urate oxidase and CN-insensitive FAOS were all found in the light mitochondrial fraction, and upon sucrose density gradient centrifugation, these activities were concentrated in the density fraction around 1.21-1.22. On the other hand, the densities of mitochondria and lysosomes were 1.19 and 1.20, respectively. From the above results, we concluded that Bombina liver contains peroxisomes. Next, the characteristics of CN-sensitive (mitochondrial) or CN-insensitive (peroxisomal) FAOS and carnitine acyltransferase activities were compared in the partially purified peroxisomes and mitochondria using various chain length fatty acyl-CoAs (C2-C20). FAOS activities of the peroxisomes were effective for long-chain fatty acyl-CoAs (C8-C16), while the mitochondrial FAOS showed broad specificity for short- to long-chain fatty acyl-CoAs. Both the peroxisomes and the mitochondria showed high carnitine acyltransferase activities for acetyl-CoA and C8 to C12 fatty acyl-CoAs. Administration of clofibrate for 7 d enhanced the activities of catalase and CN-insensitive FAOS, but the D-amino acid oxidase activity decreased and the urate oxidase activity was unchanged. The results indicate that peroxisomes do exist in Bombina liver, but the particles may be involved primarily in the exhaustive degradation of general fatty acids, not in the synthesis of bile acids. When necessary, the mitochondria and peroxisomes may act cooperatively in order to obtain energy from various fatty acids.