Branched-chain amino adds

Valine, leucine, and isoleucine are branched-chain amino adds whose metabolism is abnormal in maple syrup urine disease (discussed in Chapter 17). 

Figure 8.23 Formation of glutamine from glucose and branched-chain amino adds in muscle and adipose tissue and probably in the lung. Oxoacids may also be released into blood for oxidation in the liver.

Isoleucine is both ketogenic and glucogenic, because its metab olism yields acetyl CoA and propionyl CoA. The first three steps in the metabolism of isoleucine are virtually identical to the initial steps in the degradation of the other branched-chain amino adds, valine and leucine (see Figure 20.10). 

The reduction in the branched-chain amino adds leucine, isoleucine and valine is caused by the higher clearance rate in HE, probably as a result of a hyperammonaemia-related increase in the secretion of insulin. These amino acids compete with the aromatic amino acids for a common carrier system through the blood-brain barrier. Because of the decrease in branched-chain amino acids, more aromatic amino acids reach the brain. This process is stimulated by ammonia, (s. fig. 15.1) (s. tab. 15.1) However, such an abnormal amino acid ratio can also be found in patients without HE. 

Isoleucine, valine, and leucine are the branched-chain amino adds (BCAAs). They are indispensable (essential), but the risk of developing a dietary deficiency is low because they are plentiful in most diets. The branched-chain amino adds. In addition to phenylalanine, are the most lipophilic of the amino acids ... 

The branched-chain amino adds (BCAAs) are leucine, isoleucLne, and valine. Pathways for the breakdown cif leucine and isoleudnc appear in Figures 8,5 and... 

Branched chain amino acids. (B), alio isoleucine (B),. . 2-keto and 2-OH acids (U) Branched chain amino adds . (B), alio isoleucine (B),. .lactic and pyruvic (B,U), 2-keto glutaric. . . .. 2-keto 2-OH acids (U) . . 

Figure 23.16 PATHWAY INTEGRATION The glucose—alanine cycle. During prolonged exercise and fasting, muscle uses branched-chain amino adds as fuel. The nitrogen removed is transferred (through glutamate) to alanine, which is released into the bloodstream. In the liver, alanine is taken up and converted into pyruvate for the subsequent synthesis of glucose.

J. Stetter (ed.), Heibicides Inhibiting Branched Chain Amino Adds Biosynthesis. Recent Development [Chemistry of Plant Protection, Vol. 10], Springer-Verlag, Berlin, 1994. 

Featherston, W.R. Horn, G.W. (1973). Dietary influences on the activities of enzymes involved in branched-chain amino add catabolism in the chick. ]. Nutr., 103, 757-65. 

T. R. Hawkes, S. E. Thomas, Biosynthesis of Branched Chain Amino Adds, Balaban Publishers, Weinheim... 

Gaston, S, Ribas-Carbo, M, Busquets, S, Berry, JA, Zabalza, A, Royuela, M, Changes in mitochondrial electron partitioning in response to herbicides inhibiting branched-chain amino add biosynthesis in soybean. Plant Physiol. 133, 1351-1359 (2003). 

Aspartate Family and Branched>Chain Amino Adds... 

Maple syrap urine disease (MSUD) is an inborn error of the branched-chain keto acid dehydrogenase (BCKDH) enzyme complex required for the catabolism of the branched-chain amino adds (BCAA) leucine, valine, and isoleucine (Fig. 16.1). 

MSUD is an autosomal recessive disorder caused by deficiency of branched-chain a-ketoacid dehydrogenase (Pig. 47.1). The a-ketoadds derived from isoleucine, valine and leucine (branched-chain amino adds) accumulate and are excreted in the urine, giving it the peculiar odour of maple syrup. The branched-chain amino acids and the branched-chain a-ketoacids that accumulate in the blood are neurotoxic, causing severe neurological symptoms, cerebral oedema and mental retardation. A diet low in branched-chain amino acids is an effective treafinenL... 

These are considered anabolic and utihzable directly by the muscle fibers for their protein synthesis [106]. For patients, the precise salutary amounts and scheduling of these branch-chain amino adds are not established (see Chapter 6 in this volume). They are somewhat difficult to dissolve in liquid. 

Watson, R, Strachan, A.T., Shirreffs, S.M., and Maughan, RJ., Branched-chain amino adds and prolonged exercise capacity in a warm environment, Proc. Nutr. Soc., 61, 109A, 2002 (abstract). 

Wakai, T. and Yamamoto, N. (2013) A novel branched chain amino adds responsive transcriptional regulator, BCARR, negatively acts on the proteolytic system in Lactobacillus helveticus. PLoS One 8, e75976. 

---