The interrelationship of ribonucleic acid and protein synthesis

Clark, Catherine M (1957) The interrelationship of ribonucleic acid and protein synthesis. PhD thesis, University of Glasgow.

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Studies have been carried out on rat liver to determine the nature of the relationship between ribonucleic acid (RNA) and protein synthesis. In particular, an attempt was made to decide why the level of protein in the diet caused changes in the amount of liver RNA. The experimental studies are described in five sections, summarised as follows:- Section I. The influence of dietary protein on the incorporation of 14C-2-glycine and 32P into the ribonucleic acid of rat liver. 1. Rats were maintained on diets either containing adequate amounts of protein or free from protein, and after fasting overnight, were injected with 32P and with 14C-2-glycine. They were killed at 3, 6 and hr. thereafter. A further group of rats which had received the protein-containing diet was fed protein at the time of injection with the isotopes. 2. The uptake of glycine into liver protein was essentially similar in the two groups in the post-absorptive state, but rose considerably when protein was fed at the time of injection. 3. Labelling of RNA with 32P and with glycine was much reduced in rats fasted overnight after the protein-containing diet. On feeding protein to this group, uptake of both isotopes rose to the level found with the protein-free diet. 4. It is suggested that the low level of labelling in the groups fasted after the protein-containing diet was due to breakdown of RNA as soon as the supply of amino acids from the gut ceased, the products of breakdown causing dilution of isotopically labelled precursors of RNA in the acid-soluble fraction of liver. The feeding of protein, by restraining RNA breakdown and thus terminating dilution of these precursors, restored the level of labelling in RNA. This hypothesis is supported by a study of the effect of diet (a) on changes in the RNA content of the liver, (b) on 14C-uptake by the purines of the acid-soluble fraction of liver, (c) on the uptake of 32P by the RNA of different liver cell fractions and (d) on allantoin excretion. 5. It is concluded that the rate of synthesis of liver RNA is a function of the available energy, whereas the stability and therefore amount of RNA in the liver is determined by the supply of amino acids for protein synthesis. Section II. The uptake of 14C-2-glycine and 32P by liver ribonucleic acid when protein is administered to protein-depleted animals. 1. A study was made of the effect of feeding protein to animals fasting after a protein-free diet on the uptake of 14C-2-glycine into protein and acid-soluble purines and the uptake of 14C-2-glycine and 32P into the purines of RNA in rat liver. 2. Feeding of protein to protein-depleted animals resulted in an increase in the incorporation of 14C-2-glycine into protein and into the acid-soluble purines. Section III. The effect of feeding complete and incomplete amino-acid mixtures on the uptake of labelled precursors into the purine and pyrimidine bases of rat liver. 1. Since the feeding of protein is accompanied by a decrease in RNA breakdown, the effect of feeding amino-acid mixtures was studied. The two amino-acid mixtures fed differed only in that one contained tryptophan and was nutritionally complete, whereas the other was deficient in this amino acid. The main studies were carried out on rats which had previously been fed a protein-free diet. 2. The complete amino-acid mixture produced an increase in protein synthesis accompanied by an increased uptake of 14C-2-glycine into RNA and the acid-soluble purines, together with a gall in the G/A ration for 14C-2-glycine uptake. 3. The effect of the two amino-acid mixtures on the incorporation of 14C-6-orotic acid uptake fell when the complete amino-acid mixture was fed. Section IV. The action of B-2-thienylalanine on protein synthesis and RNA turnover in rat liver slices and cytoplasm. Section V. Studies on RNA breakdown in isolated microsomes. 1. The effects of previous diet on the breakdown of RNA in liver microsomes incubated in vitro was studied, and a few preliminary experiments have been recorded. 2. Breakdown of RNA was studied by quantitative estimation of RNA in the system (orcinol method) and by the diluent effect of adenine-containing breakdown products of RNA on the activity of the 14C-8-adenine added to the suspending medium.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: H N Munro
Keywords: Biochemistry
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-72689
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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