Studies in Protein Synthesis: The Relationship of Energy Intake to Protein Metabolism

Chisholm, James (1957) Studies in Protein Synthesis: The Relationship of Energy Intake to Protein Metabolism. PhD thesis, University of Glasgow.

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Studies have been carried out on rats to determine the nature of the relationship between the level of energy intake and protein metabolism. The experimental studies are described in five sections, summarised as follows Section 1. The influence of previous energy level on the in vitro uptake of 35S-methionine into the proteins of rat liver and muscle, 1. Rats were maintained on a diet of adequate protein content, to which had been added increasing energy increments in the form of fat, and after fasting overnight were then killed 12-14 hours or 18-20 hours later. 2. The uptake of methionine into liver and diaphragm proteins increased linearly with increasing levels of energy intake. 3. The conclusion to be drawn from this series of experiments is that previous energy intake exerts a prolonged action on protein metabolism in both liver and muscle. Section 2. The influence of previous energy intake on the in vitro incorporation of 14C-glycine into liver proteins. 1. A study was made of the influence of the energy content of diets (both protein-free and protein-containing) on the in vitro uptake of 14-C-glycine into rat liver proteins. In this instance, a comparison was made between rats which were in a post-absorptive state for 12 hours and those which had just been fed a protein meal. 2. The uptake of isotope increased as the energy content of the preceding diet rose; the influence of energy level was greater when the previous diet contained protein. 3. Since energy level exerts its greatest effect within the first hour of incubation, it is suggested that the differences in 14C-glycine incorporation may be due to differences in the rate of penetration of isotope into the cell; it is not possible from such experiments to determine whether protein synthesis per se is affected by energy level. Section 3. The influence of previous energy level on the in vivo incorporation of 14C-glycine into liver protein. 1. Rats were maintained on the same dietary regimes as those described in Section 2 and were sacrificed 3 and 6 hours after the injection of 14C-glycine. 2. The only circumstance in which the energy level in the preceding diet affected protein synthesis was in the case of the group fasting after a normal protein intake. In contrast, the energy level of the diet did not affect the uptake of glycine when the rats had been fed a protein-free diet or when the rats were in the absorptive state after a protein meal. 3. The conclusion has been drawn that differences in energy content of the diet exert their main effect on protein utilisation in the post-absorptive state and not at the time when tissues are being flooded with amino acids from the gut. Section 4. The effect of previous energy intake on the adenosine nucleotide pattern of rat liver. 1. Rats were maintained on diets either containing protein or free from protein and providing different energy levels. 2. In the post-absorptive state, the ATP/ADP ratio was found to improve when the energy content of the preceding diet was raised. Such an improvement in the ratio was obliterated when protein was fed 2 hours prior to sacrifice. 3. A difference in nucleotide pattern was still apparent even when a meal was interposed between the last energy supplement and sacrifice; again, the feeding of protein before death altered the pattern. 4. The results were interpreted to mean that the enhanced ATP/ADP ratio observed with increasing energy intakes may well regulate the incorporation of amino acids into protein and consequently the change of nucleotide pattern on feeding protein could account for the lack of influence of energy intake during the phase of absorption. Section 5. The influence of energy intake on PAH synthesis by liver slices in vitro. 1. Liver slices from rats which had been fed on the same dietary regimes as above were incubated with p-amino benzoic acid and glycine. 2. When the results are expressed in terms of the DNA content, the effect of protein and energy intake appears to increase the synthesis in the protein-fed group in the post-absorptive state. 3. When the results are expressed per mg. wet weight, it would appear that no differences exist between the various dietary fators. The fact that differences are no longer apparent has been taken to mean that energy level has no effect on PAH synthesis independent of changes in protein (i.e. enzyme) content. 5. It has been concluded that PAH peptide bond synthesis is not a suitable model system for the study of the effects of energy level on protein synthesis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physiology
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-79240
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 11:25
Last Modified: 05 Mar 2020 11:25

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