Metabolism of valine, leucine, isoleucine, and lysine

See also Amino Acids Not In Proteins, Metabolism of Serine, Glycine, and Threonine, Metabolism of Valine, Leucine, Isoleucine, and Lysine, Metabolism of Sulfur-Containing Amino Acids... 

See also Metabolism of Valine, Leucine, Isoleucine, and Lysine, Essential Amino Acids... 

Most of the prokaryotic and many eukaryotic organisms (plants) are capable of synthesizing all the amino acids present in the protein. But higher animals including man possess this ability only for certain amino acids. The other amino acids, which are needed for normal functioning of the body but cannot be synthesized from metabolic intermediates, are called essential amino acids. These must be obtained from the diet and a deficiency in any one of the amino acids prevents growth and may even cause death. Methionine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine and Lysine are the essential amino acids, however, Histidine and Arginine are considered semi essential amino acids as it can be partly synthesized by the body. 

The direct stimulation of insulin liberation "in vitro" by a number of individual amino acids indicates that secondary factors in metabolism of amino acids must be of minor importance. It certainly cannot be excluded that incorporation of the amino acids into the intracellular metabolic processes of the Q-cells is the effector mechanism. Arginine and lysine participate in the urea cycle, histidine, proline, leucine, isoleucine and valine enter the citric acid cycle. It remains completely open whether the metabolism of these substrates is operative in inducing insulin secretion. 

Valine, leucine, and isoleucine biosynthesis Lysine biosynthesis Lysine degradation Arginine and proline metabolism Histidine metabolism Tyrosine metabolism Phenylalanine metabolism Tryptophan metabolism Phenylalanine, tyrosine, and tryptophan biosynthesis Urea cycle and metabolism of amino groups... 

Figure 9-3. Fates of the carbon skeletons upon metabolism of the amino acids. Points of entry at various steps of the tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis are shown for the carbons skeletons of the amino acids. Note the multiple fates of the glucogenic amino acids glycine (Gly), serine (Ser), and threonine (Thr) as well as the combined glucogenic and ketogenic amino acids phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr). Ala, alanine Cys, cysteine lie, isoleucine Leu, leucine Lys, lysine Asn, asparagine Asp, aspartate Arg, arginine His, histidine Glu, glutamate Gin, glutamine Pro, proline Val, valine Met, methionine.

Classification of amino acids into biosynthetic families emphasizes the common origin of related metabolites and is conceptually useful in delineating regulatory relationships. Lysine, threonine, methionine, and isoleucine comprise a family of amino acids originating with aspartate. However, isoleucine is also structurally and metabolically related to the branched-chain amino acids, leucine and valine. The latter two amino acids, along with alanine, are members of the pyruvate family. The common metabolic pre-... 

The concentration in wort of the amino acids isoleucine, valine, phenylalanine, glycine, alanine, tyrosine, lysine, histidine, arginine and leucine, are considered important [37]. Changes in the concentrations of amino acids in wort will undoubtedly influence nitrogen metabolism because the yeast amino acid is principally derived from the wort amino acid. 

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