Protein Amino acid imbalance

Amino acids essential for young rats (98) and fishes (99) have been reviewed. Rats preferably eat a diet with sufficient amounts of essential amino acids rather than one that is deficient (100). Each essential amino acid, consumed in self-selection, has been reviewed (101). A protein diet with an excess of essential amino acids has been described as a poor protein diet from investigations that showed remarkable growth inhibition and occurrence of fatty fiver disease in rats (102). This is called amino acid imbalance (103). 

In the soil, an imbalance of amino acids, the presence of D-amino acids derived from microbial metabolism, or analogs and homologs of constituent protein amino acids could produce a deviation in the... 

The indication for administering BCAA in patients with hepatic encephalopathy to compensate amino-acid imbalance was proposed by J.E. Fischer et al. in 1974, and implemented parenterally. However, oral application of BCAA for an adequate treatment period also has beneficial effects on cirrhosis and HE (7.) improvement in protein tolerance and the nutritional condition, (2.) improvement in cerebral functions (II8, 122), probably due to an amelioration of liver function, (2.) stimulation of ammonia detoxification with a positive nitrogen balance (118), (4.) reduction in or normalization of AAA levels, and (5.) promotion of glutamine synthesis with a favourable effect on the cells of the immune system and on renal function. By means of BCAA, it was possible to prolong the survival time and delay the occurrence of liver failure in rats with CC -induced cirrhosis. (123, 126) However, there are diverging results, which need further clarification. In principle, the use of BCAA is considered to be a necessary form of supplementary treatment for catabolic metabolism in cirrhosis (124,125, 127, 128, 130-132), in (also latent) HE and after curative resection of hepatocellular carcinoma. (I2l) (s. p. 280)... 

Experimental alkaptonuria has also been produced in rats on a diet de-ficent in sulfur-containing amino acids (295). Similar excretory patterns were produced after additional phenylalanine, tyrosine, or their corresponding keto acids, and the condition was relieved on gi dng cysteine, but not ascorbic acid (644). Moreover the p-hydroxyphenylpyruvate excretion was much lower, relative to the homogentisic acid excretion, than in the type of ascorbate-dependent alkaptonuria studied by Sealock in the guinea pig (rats cannot in any case be made ascorbic acid-deficient). Xeuberger and Webster (644) also showed that this second type of experimental alkaptonuria could be produced in many types of amino acid imbalance, or in protein deficiency, and that the threshold intake of phenylalanine or tyrosine required to produce the condition varied with the nutritional state and also with the acid-base balance, acid urines being associated with a decreased homogentisic acid excretion (cf. also 150, 273, 787). 

Peng Y, Tews JK, Harper AE. 1972. Amino acid imbalance, protein intake, and changes in rat brain and plasma amino acids. Am J Physiol 222 314-321. 

Rogers, Q. R., The nutritional and metabolic effects of amino acid imbalances, in Protein Metabolism and Nutrition, Cole, D. J. A., Ed., Butterworths, London, 1976. 

Sidransky, H. and Vemey, E., Effect of amino acid imbalances on the stimulatory effect of L-tryptophan on hepatic protein synthesis, Amino Acids, 12, 205,1997. 

Reductions in dietary protein level may decrease milk yield and, almost invariably, non-protein nitrogen content. Milk protein is httle affected until intake of protein falls below 60 per cent of requirement. This is probably due to an insufficiency of essential amino acids, primarily methionine, followed by threonine and tryptophan. When duodenal amino acid supply has been measured and deficient amino acids infused directly into the bloodstream, there have been large increases (approximately 5-8 g/kg) in milk protein content. The prediction of the amino acid profile at the small intestine in dairy cows is fraught with difficulties, and feeding studies that have attempted to rectify amino acid imbalances through supplementation have produced variable results. 

Polypeptide synthesis depends on an adequate supply of tRNAs charged with the 20 protein amino acids and appropriate interactions between their anticodons and the codons of mRNA. Peptide chain elongation is decreased or inhibited by lack of amino acids or other conditions giving rise to an imbalance or deficiency in aminoacyl-tRNAs. 

A condition in which the dietary supply of amino acids is poorly utilized in meeting the body s requirements. An amino acid imbalance usually occurs when the total protein intake is low, and there are excesses of certain amino acids while others are deficient. 

Amino acid imbalances—One type of amino acid imbalance arises when the addition of a single amino acid or mixture of amino acids to a diet reduces the utilization of the dietary protein. Even a small increase in the concentrations of certain amino acids can increase the needs for others when the total protein intake is low. 

Not enough is presently known about the practical bearing these observations may have in relation to human diets but they must be taken into account in studies of the biological effectiveness of essential amino acid patterns. Circumstances in which amino acid imbalances would occur are unlikely in individuals at normal levels of dietary protein. 

The different responses between titration strategies in Experiment 1 indicate variation in the rate of adaptation of metabolic processes triggered by changes in amino acid imbalance (e.g. protein... 

An imbalance of amino acids in the blood often alters the rate of transport of these compounds into the brain, thereby affecting levels of neurotransmitters and rates of protein synthesis 670... 

Excesses of amino acids are not harmful—with few- exceptions. An imbalance of amino acids can result in a few instances. For example, a rat that feeds on eggwhite proteins with threonine orisoleucine added in high concentrations can experience an undesirable imbalance. 

In mammals, muscle breakdown or excess protein intake results in an imbalance between the fates of the carbon chains and the amino nitrogen. Unlike fat (lipid storage) or glycogen (carbohydrate storage), excess amino acids are not stored in polymeric form for later utilization. The carbon chains of amino acids are generally metabolized into tricarboxylic acid (TCA) cycle intermediates, although it is also possible to make ketone bodies such as acetoacetate from some. Conversion to TCA intermediates is easy to see in some instances. For example, alanine is directly transaminated to pyruvate. 

Radioactive amino acids are commonly used to follow protein synthesis. The procedure is in general similar to that used to follow synthesis of DNA, but in this case the cell s growth medium already contains high concentrations of amino acids and so the added radioactive amino acid acts as a tracer without causing imbalance. However, when it is desired to increase the extent of radioactive incorporation the presence of amino acids in the growth medium may be a disadvantage and their concentration may be reduced. Drastic reduction is obviously deleterious to cell growth ( 11.7] and preliminary experiments must be performed to ascertain what reduction can. be tolerated under the experimental conditions. 

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