Summary
Actinomycin D reduced the in vivo labelling of liver RNA by tritiated methyl or ethyl carbamates. Fractionation of the RNA from mice injected 24 h previously with [3H] methyl carbamate, [2-3H] ethyl carbamate or ethyl [carboxy-14C] carbamate on MAK columns, sucrose density gradients and calcium phosphate columns or by polyacrylamide gel electrophoresis showed radioactive esters of cytosine-5-carboxylic acid to be present in the fractions where rapid RNA synthesis had occurred. This suggests that the cytosine-5-carboxylates were synthesised from these carbamates, or their metabolites, before incorporation into RNA chains or that the rapidly labelled RNA was more susceptible to attack by a chemically active metabolite from the carbamates. There was a greater incorporation of the non-carcinogenic methyl carbamate than of the carcinogenic ethyl carbamate 24h after injection. The methyl ester also caused a more rapid breakdown of RNA than ethyl carbamate, ethyl and probably methyl carbamate also increased RNA synthesis.
Zusammenfassung
Leber-RNS von männlichen NMRI-Mäusen, die 24 Std nach Injektion von (3H)Methylcarbamat, (2-3H) Äthylcarbamat oder Äthyl-(carboxy-14C)-carbamat durch Phenolextraktion nach Georgiev gewonnen wurde, enthielt carboxyalkyl-markierte Methylbzw. Äthylester der Cytosin-5-carboxylsäure. Die in vivo-Reaktion der Carbamate mit Leber RNS wurde durch Actinomycin D gehemmt. Bei der Fraktionierung durch Dichtegradientenzentrifugation, Polyacrylamidgelelektrophorese sowie Säulenchromatographie über Hydroxylapatit und Methylalbumin-Kieselgur wurde der überwiegende Teil der Aktivität (80%) in den Fraktionen gefunden, die neu synthetisierte RNS enthalten. Es ist deshalb anzunehmen, daß die Cytosin-5-carboxylate aus den Carbamaten oder ihren Metaboliten vor der Inkorporation in die RNS-Kette gebildet werden, oder daß die RNS in der Synthese-Phase gegenüber der Einwirkung chemisch aktiver Carbamatmetabolite empfindlicher ist. Das nicht carcinogene Methylcarbamat wurde dabei etwa 10fach stärker inkorporiert als das carcinogene Äthylcarbamat. Synthese- und Umsatzgeschwindigkeit der Leber-RNS wurden durch beide Carbamate etwa ihrer Inkorporationsrate entsprechend gesteigert.
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We wish to thank Professor E. Boyland and Professor W. Schmid for advice and encouragement, and Miss H. Radler and Mrs. U. Pankow for excellent technical assistance.
This investigation was supported by grants to the Chester Beatty Research Institute, Institute of Cancer Research: Royal Cancer Hospital, from the Medical Research Council and the Cancer Research Campaign.
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Williams, K., Kunz, W., Petersen, K. et al. Changes in mouse liver RNA induced by ethyl carbamate (urethane) and methyl carbamate. Z. Krebsforsch. 76, 69–82 (1971). https://doi.org/10.1007/BF00304289
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DOI: https://doi.org/10.1007/BF00304289