The hormonal control of protein synthesis. A study of the action of carbohydrate on protein metabolism

Section 1: The effect of carbohydrate and fat on the N retention of the fasting rat. 1. Experiments are described on adult rats, which had been stabilised on a protein-containing or a protein-free diet and after a 24 hour fast received either water, glucose or olive oil. 2. Carbohydrate administration significantly reduced the urinary M output in both dietary groups. Fat administration decreased the urinary E output to a less significant degree. 3. The protein M content of the liver was significantly reduced after carbohydrate administration. Fat administration did not significantly reduce the protein 1 content of the liver. 4. It was concluded that the feeding of carbohydrate resulted in N retention in the body in tissues other than the liver. Section 2: The uptake of 35S-methionine by liver and muscle protein after carbohydrate and fat administration. 1. A study was made of the effect of feeding glucose or olive oil on the incorporation of injected 35S-methionine the protein of the skeletal muscles and the livers of fasting rats. 2. It was found that neither glucose nor fat had any effect on the uptake of the labelled amino-acid by the liver. However, it was observed that glucose, but not fat, stimulated the uptake of 35S-methionine by skeletal muscle. Two hours after glucose feeding, the isotopic concentration was lower than that of e, fasting animal but the rate of appearance of the label increased more quickly than in the control until the isotopic concentration was significantly greater at the 6th hour. It was concluded that the amino-acids disappearing from the blood after glucose administration are deposited in muscle. Section 3: The effect of glucose and fat on the incorporation of 14C-2-glycine into the proteins of skeletal muscle and liver. 1. The specific activity of the free glycine pool of liver and muscle were examined, after glucose or fat Ingestion. 2. It was found that the specific activity of the free glycine pool of liver and muscle did not change significantly after water or fat administration. It was also found that carbohydrate ingestion did not alter the pattern of changes in the liver free glycine pool, while the muscle free glycine specific activities were elevated significantly above the control values, especially at the 4th and 6th hour. 3. The ratio of the muscle to liver whole protein radioactivity of the glucose-fed animals was initially below the control level but increased steadily to reach a higher value than the control some 6 hours after feeding. 4. It was cono3.uded that the changes in 14C-glycine and 35S-methionine deposition in muscle protein 4-6 hours after glucose administration were reflections of changes in - the labelling of the free amino-acid pool. Since the change in blood amino-acid level is maximal 1-2 hours after glucose feeding, it was concluded that some intermediate compound, such as a labile peptide or protein is deposited in the muscle and its subsequent breakdown causes the observed changes in amino-acid pool radioactivity. Section 4: The analysis of the acid-soluble fraction of skeletal muscle and liver after feeding: glucose, 1. Trichloracetic acid and tungstic acid extracts of muscle and liver were analysed for aniino-N by various methods. 2. Folin's ? -naphthaquinone method was found to be unreliable by the use of ion-exchange resins. 3. The ninhydrin titrimetric decarboxylation method failed to reveal any changes in the free or peptide amino-H content of the acid-soluble fractions of muscle and liver after glucose administration. These findings were confirmed by the colorimetric ninhydrin method. 4. It was concluded that glucose ingestion did not cause the temporary deposition of an acid-soluble peptide in muscle. Section 5: The examination of liver and muscle protein after glucose administration. 1. The treatment of the liver and muscle homogenate to obtain pure protein was reconsidered; in particular the stages involving heating in TCA and dissolving in NaOH. 2. It was found that, in animals injected with 14C-2-glyeine, a greater amount of radioactivity was present in the muscle protein of a glucose-fed animal, when the hot TCA and NaOH treatment was omitted. The radioactivity of the liver protein was unaltered when the hot TCA and NaOH treatment was omitted, whether or not the animal received glucose. It was therefore concluded that a SCA-labile protein is deposited in muscle following glucose administration. 3. The analysis of the hot TCA extract of muscle protein revealed that, after feeding glucose, more amino-N could be removed from the muscle protein than from the protein of the water fed control. The maximum amount of this extra amino-N occurred 2 hours after feeding glucose and fell to below control level 6 hours after feeding. 4. The hot TGA labile protein fraction of muscle was not demonstrable after 14C-1-leucine injection. 5. It was concluded that labile muso3.e protein occurred immediately after glucose administration, and that the observed dissimilarities between the uptake of 14C-glyoine and 14C -leucine are different expressions of the same mechanism