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Pronounced endogenous amino acid imbalance was seen in liver tissue and blood serum of rats kept from day 15 to day 21 of life on formula liquid diet which contained bovine serum as protein component. No disorders were found in the free amino acid ratio in liver tissue of animals who had received liquid diet in which the protein component was represented by casein (73 %) and milk serum proteins (27 %). The data obtained have been considered from the standpoint of specific requirements to the quality of milk proteins that supply the newborns with indispensable amino acids.

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In experiments on an isolated liver of animals ion-exchange chromatography of the concentration of free amino acids in the perfusate has shown that amino acids with branched chains are metabolized by the liver tissue to a less measure than other amino acids. Under high protein diet the liver capacity for metabolizing most amino acids, except valin, leucin and isoleucin is increased. The data obtained are discussed from the standpoint of transformation of amino acids with branched chains.

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Proteolysis of milk proteins occurring within the gastrointestinal tract was distinctly manifested in young rats during the period of milk feeding as shown by gel filtration of nitrogenous components from contents of various parts of small intestine of 3, 20 and 30 days old rats as well as by means of ion exchange chromatography of free amino acids and estimation of their concentration and the rate of the amino acids liberation after incubation of the content of these parts of the intestine in vitro. In 3-20 days old rats the cavitary proteolysis was competed in the distal part of small intestine, in adult animals--in the proximal part. The amino acids might be divided into two groups: the rapidly liberated substances (leucine, isoleucine, lysine, arginine, tyrosine, serine) and the slowly liberated compounds (proline, glutamic and aspartic acids). The data obtained suggest the existance of two types of protein digestion--cavitary and intracellular (and/or membrane type) during this period of the ontogenesis; concepts of alimentary specificity of caseins are also discussed.

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In simulated tests on rats of the 1st months of life set up for the purpose of educing causes accounting for a highly effective utilization of the milk proteins in the early post-natal perions subject to study were the amino acids metabolism rates. An investigation of the enzymes activity showed that a falling of the milk proteins utilization effectiveness proceeds against the background of an intensive inclusion of the catabolic route of the amino acids metabolism in the liver. The urea content in the urine correlated with a gradual inclusion of the enzymatic liver systems partaking in the urine formation. The amino acids metabolism with a ramified chain in the liver tissue of rats of the first days of life was found to stand low to a still greater degree than this was the case in adult animals. One of the causes responsible for a highly effective utilization of the milk proteins in the perinatal period may be due to an incomplete functioning of the catabolic route of the amino acids metabolism in the liver.

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It is found that in the period of the 1st to the 20th day of life there takes place shifting of the cavitary digestion of milk proteins toward the distal part of the small intestine. The change-over from the milk to the definite alimentation is accompanied by a shift of the process of the milk proteins digestion to the proximal part of the small intestine. The jejunum chyme of the 3, 12 and 20-day old rats contains roughly equal amounts of free amino acids, whereas in the jejunum chyme of the 30-day old animals their concentration is twice as high. The results of determining the speed of the amino acids release in tests with incubation in vitro of the jejunum chyme in 3, 12 and 20-day old rats bear proof to the existence at the young age of two types of digestion, viz. of the cavitary and intracellular (and/or membranous).

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The assimilation of milk proteins in dynamics by rats during the first 23 days of their life was studied. During this time the animals were kept on a natural milk feeding and were denied the maternal one. Data on the amount of consumed protein and on an increase of the protein content in the carcass in 2- and 4-day long intervals served as a basis for determining the degree of effective utilization of protein (U) by rats. It is shown that the degree of the food protein, while remaining at a high level, experienced certain changes. It is possible to distinguish three periods in the change of this value: the first--starting from birth up to 5 days, with U rising from 74,5 up to 92.1 per cent, the second period, the milk diet proper,--up to the 15th day, marked by a high value of U (approximately 93 per cent) and, finally, the third period--transitional to the ration of an adult animals--marked by a drop of U down to 67.8 per cent. The data obtained may be used in considering issues related to features specific for the processes of the protein assimilationin in the early post-natal period.

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Following determination by the method of ion-exchange chromatography of free amino acids in the blood drawn from the portal and liver veins and the abdominal aorta 30 minutes after introduction of a casein suspension to rats it was found that only 50 per cent of amino acids with ramified chain are retained in the liver. Most of the other amino acids, however, become metabolized largely in the liver and it is only their insignificant part that goes into the general circulation. These data may be of use in considering problems related to the peculiarities of metabolism of amino acids with ramified chain.

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By summarizing the results of their personal experimental research work and literature sources the authors come to the conclusion that a temporal determination of the free amino acids concentration in the portal vein blood of rats enables one to judge about the summary duration of the first two stages of the protein assimilation, namely about the rate of the protein digestion and that of the amino acids absorption. The aminogram of free amino acids in the blood of the portal vein shows a marked tendency toward convergence with the consumed protein aminogram.

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Alteration in pH and addition of urea (final concentration 3 M) did not affect the electrophoretic and chromatographic separation of glycomacropeptide. At the same time, urea (5 M) distinctly increased an amount of beta-component in separation by free electrophoresis. Sedimentation constant SO2OW and molecular weight of glycomacropeptide were equal to 1.35 S and 13000, respectively. Both fractions of glycomacropeptide had similar amino acid composition and contained phosphorus (0.4%). The variations were observed in the carbohydrate components of the molecules. The heavy component contained 5-fold higher concentration of sialic acids (9.7-9.6%), 2-fold higher concentration of galactose (13%) and acetyl galactosamine (5.0-4.0%) as compared with the beta-component (3.1-0.9%, 7.5% and 2.5%, respectively). These alterations in carbohydrate component of glycomacropeptide were suggested to affect the polymeric conformation of the molecule.

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It has been ascertained that the blood serum of individuals fasting for 20 days demonstrates a sharply pronounced derangement in the proportions of amino acids, i. e. a manifestation of an endogenous amino acids imbalance. The most steep is the rise in the content of isoleucine, leucine and valine. These data may be used in considering issues concrened with an upset metabolism of amino acids under conditions of endogenous alimentation.

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