Abstract
Studies were made on the sedimentation analyses of rat liver ribosomes and polyribosomes after intraperitoneal administration of actinomycin D.Don-Ryu rats,150-200g body weight, were fasted for 9-12 hours before use. Actinomycin D was injected into intraperitoneal cavity ( 2 mg/kg body weight), and they were killed 0,3,6,9,12,18 and 23 hours after the injection of actinomycin D.Rat liver polyribosomes were analysed by the sucrose density gradient centrifugation method [0.5 M-1.5 M-sucrose-TKM buffer (0.5 M-1.5 M-sucrose containing 0.05 M-Tris-HCl, pH 7.5, at 20°C; 0.025 M-KCl; 0.005 M-MgCl2)], and also by the band sedimentation method using a Spinco Model E analytical centrifuge.After 3 hours, heavy polyribosomes decreased markedly in amount, while monosomes and disomes increased gradually. After 18 hours, however, monosomes also started to decrease.It has been suggested by a number of authors that actinomycin D probably inhibits the synthesis of messenger RNA (m-RNA) and accelerats the degradation of m-RNA, thus resulting in the decrease in the amount of heavy polysomes and the increase in the amount of light polysomes or monosomes. Our results are in agreement with these suggestions.It is calculated from my results that the half life of the hepatic m-RNA is about 6 hours.
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