Catabolism basic amino acids

A substrate is a substance that is the basic component of an organism. Protein substrates are amino acids, which are essential to life Protein substrates are amino acid preparations that act to promote the production of proteins (anabolism). Amino acids are necessary to promote synthesis of structural components, reduce the rate of protein breakdown (catabolism), promote wound healing, and act as buffers in the extracellular and intracellular fluids. Crystalline amino acid preparations are hypertonic solutions of balanced essential and nonessential amino acid concentrations that provide substrates for protein synthesis or act to conserve existing body protein. 

Matsuda et al. (27) showed that the adenylosuccinate synthetase basic isozyme has a lower Km for aspartate, is more sensitive to inhibition by fructose 1,6-bisphosphate, and less sensitive to inhibition by nucleotides than the acidic isozyme. These properties could indicate that the basic isozyme is regulated coordinately with glycolysis (or gluconeogenesis) as proposed for the operation of the purine nucleotide cycle in skeletal muscle. The enzyme could also be affected by the availability of aspartate, as was found in Ehrlich ascites cells. The increase in basic isozyme activity, under conditions used in this study where the animal must rely on protein for most of its energy, is consistent with the idea that it is involved in the purine nucleotide cycle. This probably is not as an alternative to glutamate dehydrogenase in urea synthesis but is simply in amino acid catabolism. The small... 

In addition to the fatty acids with straight (unbranched) chains and an even number of C atoms, small amounts of acids with branched methyl groups or with an odd number of C atoms are also found in nature. Their metabolic fate in jS-oxi-dation is of considerable interest and can best be studied on the examples of the methyl branched C4- and the Ce-carboxylic acids. These two acids arise from the catabolism of the amino acids leucine, isoleucine, and valine by transamination and oxidative decarboxylation, as described in Chapt. VIII-10. Basically only two situations need to be discussed one with a methyl group in the a-position, or potentially in a-position (i.e. by repeated shortening of the chain by two C atoms the methyl group eventually ends up in a-position) the other with a methyl group in the -position, or at least potentially in /3-position. 

LAB are able to produce many important aroma cort iounds from amino acid (AA) catabolism (Table 19.1). LAB possess a powerful proteolytic system, in relation to their multiple auxotrophy for AA, which has been reviewed in detail (Fox and Wallace 1997 Christensen et al. 1999 Smit et al. 2005 Steele et al. 2013). LAB hydrolyze proteins into peptides and amino acids, which impact the taste of foods. Large hydrophobic peptides are associated with (undesirable) bitter taste, while peptides and A A contribute to the basic taste of cheese. The hydrolysis of large hydrophobic peptides can be accelerated by the release of intracellular peptidases from lysed LAB cells in cheese paste, in which they remain active during the ripening period, thus decreasing cheese bitterness (McSweeney and Sousa 2000). 

In some instances, combinations of Cig and silica columns are also used for better purification of the crude extracts (431, 445). A combination of Cg, silica, and amino solid-phase extraction columns has been successfully employed to fractionate anabolic and catabolic steroid hormone residues from meat in polar and nonpolar neutral and phenolic compounds, and to purify further each fraction effectively (452). Another combination of two solid-phase extraction columns, one using a graphitized carbon black sorbent and the other Amberlite resin in the hydroxyl form, allowed neutral anabolics to be isolated and separated from acidic anabolics and their metabolites (453). A combination of basic alumina column placed in tandem with an ion-exchange column has also been applied for the purification of the crude extracts in the determination of diethylstilbestrol and zeranol (427), and estradiol and zeranol in tissues (450). 

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