Alanine kidney amino acid

Major amino acids emanating from muscle are alanine (destined mainly for gluconeogenesis in liver and forming part of the glucose-alanine cycle) and glutamine (destined mainly for the gut and kidneys). 

Flavin Coenzymes.—5-Deazaflavin-adenine dinucleotide (2) can be prepared from the 5-deazaFMN,21 using a FAD pyrophosphorylase from rat liver.22 When the apoprotein of D-amino-acid oxidase from pig kidney is reconstituted with (2), no oxidation of D-alanine is observed, although the flavin chromophore in the reconstituted enzyme is reduced on the addition of DL-amino-acids.22 This has been interpreted as indicating that hydrogen transfer from the amino-acid to (2) can still... 

Amino groups released by deamination reactions form ammonium ion (NH " ), which must not escape into the peripheral blood. An elevated concentration of ammonium ion in the blood, hyperammonemia, has toxic effects in the brain (cerebral edema, convulsions, coma, and death). Most tissues add excess nitrogen to the blood as glutamine. Muscle sends nitrogen to the liver as alanine and smaller quantities of other amino acids, in addition to glutamine. Figure I-17-1 summarizes the flow of nitrogen from tissues to either the liver or kidney for excretion. The reactions catalyzed by four major enzymes or classes of enzymes involved in this process are summarized in Table T17-1. 

The main precursors of gluconeogenesis in the liver are lactate from anaerobically working muscle cells and from erythrocytes, glucogenic amino acids from the digestive tract and muscles (mainly alanine), and glycerol from adipose tissue. The kidney mainly uses amino acids for gluconeogenesis (Glu, Gin see p.328). 

The skeletal muscle is the most important site for degradation of the branched-chain amino acids (Val, Leu, lie see p. 414), but other amino acids are also broken down in the muscles. Alanine and glutamine are resynthesized from the components and released into the blood. They transport the nitrogen that arises during amino acid breakdown to the liver (alanine cycle see above) and to the kidneys (see p. 328). 

Figure 32-3. Schematic representation of fuel mobilization during fasting. Catabolism of muscle proteins provides alanine for gluconeogenesis and glutamine for utilization by the gut and kidney, while branched chain amino acids are primarily oxidized within the muscle. Breakdown of adipocyte triacylglycerols provides glycerol and free fatty acids (not shown) the free fatty acids provide fuel for liver, muscle and most other peripheral tissues. The liver utilizes both alanine and glycerol to synthesize glucose which is required for the brain and for red blood cells (not shown). Adapted from Besser and Thirner (2002).

Resolution of DL-alanine (1) is accomplished by heating the N-acetyl derivative (2) in weakly alkaline solution with acylase, a proteinoid preparation from porcine kidney containing an enzyme that promotes rapid hydrolysis of N-acyl derivatives of natural L-amino acids but acts only immeasurably slowly on the unnatural o-isomers. N-Acetyl-DL-alanine (2) can thus be converted into a mixture of l-( + )-alanine (3) and N-acetyl-o-alanine (4). The mixture is easily separable into the components, because the free amino acid (3) is insoluble in ethanol and the N-acetyl derivative (4) is readily soluble in this solvent. Note that, in contrast to the weakly levorotatory o-( - )-alanine (a 14.4°), its acetyl derivative is strongly dextrorotatory. 

Cellular accumulation of D-fructose is inhibited by the presence of glycine, L-hydroxyproline, L-lysine, and L-phenylalanine. There is a well known relationship between transport systems for hexose and amino acid in intestine and kidney.22-25 D-Fruetose inhibits transport of L-alanine and glycine in rat intestine, but has no effect on transport... 

Fig. 42.3. Interorgan amino acid exchange after an overnight fast. After an overnight fast (the postabsorptive state), the utilization of amino acids for protein synthesis, for fuels, and for the synthesis of essential functional compounds continues. The free amino acid pool is supported largely by net degradation of skeletal muscle protein. Glutamine and alanine serve as amino group carriers from skeletal muscle to other tissues. Glutamine brings NH4 to the kidney for the excretion of protons and serves as a fuel for the kidney, gut, and cells of the immune system. Alanine transfers amino groups from skeletal muscle, the kidney, and the gut to the liver, where they are converted to urea for excretion. The brain continues to use amino acids for neurotransmitter synthesis.

Most tissues transfer the amino acid nitrogen to the liver to dispose of as urea. They, therefore, produce either alanine (from the pyruvate-glucose-alanine cycle, in skeletal muscle, kidney, and intestinal mucosa) or glutamine (skeletal muscle, lungs, neural tissues) or serine (kidney), which are released into the blood and taken up by the liver. 

In addition to acylation, there appear to be other modes by which LAL is metabolized in the kidney. Engelsma et al. (88) reported the oxidation of LAL by 1-amino acid oxidase. The oxidation of L,D-lysinoalanine resulted in the formation of 3-(piperi-donyl)-alanine. It was suggested, but not proven, that 2-(piperi-donyl)-acetic acid would be the product of the oxidation of L,L-lysinoalanine. Later, Leegwater and Tas 89) suggested that when L,L- and L,D- LAL are treated with 1-amino acid oxidase in the presence of catalase the products are the 6S, 8S and 5R, 8R enantiomers of 1,7-diazabicyclo-[3.3.0]nonane-6,8-dicarboxylic acid. 

Peptide hormones are produced by the endocrine glands (pituitary, thyroid, pineal, adrenal, and pancreas) or by various organs such as the kidney, stomach, intestine, placenta, or liver (Table 3.4). Peptide hormones can have complex, convoluted structures with hundreds of amino acids. Figure 3.2 illustrates the chemical structure of human insulin and its three-dimensional shape. Insulin is made of two amino acid sequences. The A-Chain has 21-amino acids, and the B-Chain has 30-amino acids. The chains are linked together through the sulfur atoms of cysteine (Cys). Peptide hormones are generally different for every species, but they may have similarities [11]. Human insulin is identical to pig insulin, except that the last amino acid of the B-Chain for the pig is alanine (Ala) instead of threonine (Thr) (lUPAC and lUBMB) [9] and [11]. 

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