The purpose of the experiments was to reveal the contribution of ribonuclease (RNase) activity, the enrichment of the size and amount of polysomes, and to the enhancement of protein synthesis occurring in the liver after x-irradiation. The time dependence of RNase activity was studied between 2 and 30 hr after whole-body x-irradiation of guinea pigs with 3000 R. As found, RNase activity dropped to its minimum in deoxycholate (DOC)-treated liver microsomes at 15 hr. Accordingly, fewer polysomes degraded than in unirradiated controls, as shown by the size distribution of polysomes in the pattern obtained by sucrose density gradient centrifugation. The dose dependence experiments were performed at 15 hr after x-irradiation. In microsomes not treated with DOC the alkaline free RNase did not change appreciably up to 3000 R and the total alkaline RNase activity decreased slightly between 500 and 1500 R. In microsomes treated with DOC the free RNase activity decreased appreciably and the total RNase activity slightly as a function of the dose up to 1500 R. The amount of RNase-inhibitor (RI)-bound alkaline RNase in microsomes not treated with DOC decreased slightly; in DOC-treated microsomes it rose three- to four-fold up to 800 R. The RI-content in the supernantant of unirradiated control liver microsomes was ten times higher than the total RNase activity. Also at 15 hr the RI-content rose slightly with the increasing dose. The microsomal acidic RNase activity did not show any appreciable change 15 hr after 3000 R irradiation. Authors discuss what role the decrease of RNase activity plays in the enrichment in size and amount of liver polysomes and of RNA in vivo in addition to the earlier confirmed RNA synthesis.

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