title: Alterations in the enzyme activity and polypeptide composition of rat hepatic endoplasmic reticulum during acute exposure to 2-acetylaminofluorene.
abstract: Studies have been made of the morphology, enzyme activity and protein composition of liver endoplasmic reticulum in rats exposed to acute doses of the carcinogen, 2-acetylaminofluorene (2-AAF). Electron microscopic examination revealed numerous ultrastructural changes in the hepatocyte; most consistent alterations were the disorganisation of endoplasmic reticulum system with apparent increase of smooth endoplasmic reticulum. Administration of 2-AAF to rats immediately depressed microsomal glucose-6-phosphatase activity and eventually induced epoxide hydratase activity 6--7-fold over control activity. The induction was time-dependent and maximal rates of induction were observed at dosages greater than 40 mg/kg body wt. The treatment also induced cytochrome b5 content, NADH and NADPH cytochrome c reductase activities (1.0--1.5-fold). Only very small changes in the total content of cytochrome P-45- were noted. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of microsomal proteins from 2-AAF pretreated animals showed time-dependent induction of two polypeptides which differed slightly in migration, in the region of Mr = 48000; the fast-migrating induced polypeptide has been identified as epoxide hydratase. Two-dimensional PAGE analysis of microsomal proteins from 2-AAF exposed rats showed a reproducible deletion of a protein with molecular weight in the region of 67000. The basis for the alterations in the protein composition of endoplasmic reticulum in response to 2-AAF treatment is discussed.
mesh_terms: D015073:2-Acetylaminofluorene / Q000633:toxicity*; D000818:Animals; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D010455:Peptides; D015073:2-Acetylaminofluorene