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Turnover of messenger RNA, apoprotein and haem of cytochrome P-450b + e induced by phenobarbitone in rat liver.

ABSTRACT: A single injection of phenobarbitone elicits asynchronous behaviour in the pattern of induction of mRNA, apoprotein and haem of cytochrome P-450b + e. The mRNA content reaches a maximum around 16h, the apoprotein content reaches a maximum around 30-36h, and the holoprotein content shows biphasic behaviour, with maxima around 16h and 30-36h. With the use of CoCl2 to block fresh transcription of cytochrome P-450b + e mRNA, the half-life of the preinduced mRNA was found to be 3h. The apoprotein and haem moieties of cytochrome P-450b + e turn over with half-lives of 16h and 8h respectively. The pattern of induction of delta-aminolaevulinate synthase shows biphasic behaviour, with maxima around 16h and 30-36h. The biphasic behaviour of the holoprotein content is thus due to differences in the extent of saturation of the apoprotein with haem, the process being regulated by the activity of the rate-limiting delta-aminolaevulinate synthase and the independent faster turnover rate of haem with respect to the apoprotein. Massive degradation of the haem moiety of preformed cytochrome P-450b + e results in the subsequent degradation of the apoprotein.

SUBMITTER: Ravishankar H

PROVIDER: S-EPMC1145151 | biostudies-other | 1985 Jul

REPOSITORIES: biostudies-other

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Project description:1. The regulation by testosterone of mRNA complexity and mRNA activity was investigated in rat caput and cauda epididymidis. 2. The sequence complexity of cytoplasmic poly(A)-containing RNA from normal rats was determined by homologous hybridization with radiolabelled complementary DNA probes by using RNA in excess. Computer analysis of results suggested that hybridization could best be described by curves composed of two components distinguished by their relative abundance. Thus caput-epididymidal RNA consists of approx. 260 moderately abundant and 16400 scarce sequences, whereas cauda-epididymidal RNA consists of approx. 124 moderately abundant and 13400 scarce sequences. Judging by heterologous-hybridization reactions, castration did not result in appreciable alterations in either sequence complexity or the relative abundance of the two classes of poly(A)-containing RNA. 3. To investigate if individual mRNA sequences were regulated by androgens, mRNA was translated in a cell-free system derived from reticulocyte lysate. Since most of the translation products had a different mobility on sodium dodecyl sulphate/polyacrylamide gels from the authentic proteins synthesized in tissue minces, antibodies were used to identify specific translation products. Antibodies to the two related major proteins (mol.wt. 18500 and 19000) secreted by the caput epididymidis and whose synthesis is stimulated by testosterone both precipitated a single translation product of mol.wt. 21000. That this polypeptide was a precursor to the secreted proteins was suggested by the fact that the addition of microsomal membranes isolated from dog pancreas resulted in the appearance of a polypeptide of mol. wt. 19000. 4. Translation of RNA from the caput epididymidis of rats of different hormonal status showed that mRNA activity for the 21000-dalton polypeptide declined after castration, but could be restored by treating rats with testosterone. 5. It is concluded that testosterone stimulates the synthesis of a major protein secreted by the caput epididymidis by regulating its mRNA activity.

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Turnover of messenger RNA, apoprotein and haem of cytochrome P-450b + e induced by phenobarbitone in rat liver.

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