title: Effect of extra-hepatic Walker sarcoma 256 on the synthesis and degradation of liver cytochromes P-450 and b5.
abstract: Extra-hepatic Walker sarcoma 256 produced a marked decrease (approximately 60%) in the levels of cytochrome P-450 and NADP-cytochrome P-450 reductase in rat liver endoplasmic reticulum, and a lesser decrease (approximately 20%) of cytochrome b5 and NADH-cytochrome b5 reductase. Polychlorinated biphenyls induced the synthesis of these cytochromes and reductases to approximately the same extent both in normal and tumor-bearing rats. The double-label technique was used to demonstrate that the synthesis of cytochromes P-450 and b5 was reduced in the liver of tumor-bearing rats. The turnover of P-450 was not affected by the tumor, whereas cytochrome b5 turnover was decreased. It is proposed that Walker sarcoma 256 mainly affects the transcription of cytochromes P-450 and b5 through a toxohormone, and that a regulatory mechanism coordinates the level of each cytochrome and its respective reductase.
mesh_terms: D000818:Animals; D002279:Carcinoma 256, Walker / Q000201:enzymology*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003579:Cytochrome Reductases / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism*; D005260:Female; D008862:Microsomes, Liver / Q000201:enzymology*; D011078:Polychlorinated Biphenyls / Q000494:pharmacology; D051381:Rats
chemical_list: D003573:Cytochrome b Group; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D003579:Cytochrome Reductases