Amino acids breakdown

An alternative to the extraction of intact PHA polymer is the isolation of PHA monomers, oligomers, or various derivatives such as esters [74]. PH As are composed of stereo-chemically pure P-3-hydroxyacids, and therefore can be used as a source of optically pure organic substrates for the chemical and pharmaceutical industry [79]. In this protocol, the defatted cake containing PHA polymer would be chemically treated to obtain the PHA derivatives. For example, transesterification of the meal with methanol would give rise to methyl esters of 3-hydroxyalkanoic acids. The PHA derivatives would then be separated from the meal with appropriate solvents. One potential disadvantage of this method is the potential alteration of the quality of the residual meal if the harsh chemical treatments required for the production of PHA derivatives lead to protein or amino acid breakdown. 

Figure 8.16 The control of amino acid breakdown and protein synthesis in liver. The factors in regulation are as follows (i) the amino acid concentration in the blood regulates the rate of urea production (Chapter 10) (ii) the amino acid leucine, and the anabolic hormones increase the rate of protein synthesis. Mass action is a term used to describe the effect of concentration of substrate on the reaction rate. The control of protein synthesis is discussed in Chapter 20. Control by leucine has been studied primarily in muscle.

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). 

The pathways of amino acid catabolism are quite similar in most organisms. The focus of this chapter is on the pathways in vertebrates, because these have received the most research attention. As in carbohydrate and fatty acid catabolism, the processes of amino acid degradation converge on the central catabolic pathways, with the carbon skeletons of most amino acids finding their way to the citric acid cycle. In some cases the reaction pathways of amino acid breakdown closely parallel steps in the catabolism of fatty acids (Chapter 17). 

Barker, H. A., Amino acid degradation by anaerobic bacteria. Ann. Rev. Biochem. 50 23, 1981. A review of an important group of fermentation pathways of amino acid breakdown that occur in nature and could not be covered in this chapter. 

Some of the diseases of amino acid catabolism are listed in table 22.3. These naturally occurring defects have been invaluable in demonstrating the obligatory nature of some of the steps in amino acid breakdown. A mutation that causes a defective enzyme usually leads to (1) a substantial accumulation of the intermediate that is a substrate for that enzyme, and (2) a drastic lowering of all the intermediates below that step in the pathway. 

When tissues are hypoperfused, the resulting anaerobic conditions have energetic consequences. First, all catabolic processes that require an active ETS and oxidative phosphorylation (e.g., -oxidation of fatty acids and amino acid breakdown) are inhibited. Thus, certain energy stores cannot be... 

What is the fate of the carbon skeleton in amino acid breakdown ... 

What is the fate of the carbon skeleton in amino acid breakdown The catabohsm of amino acids has two parts the fate of the nitrogen and the fate of the car-... 

What is the role of the urea cycle in amino acid breakdown In the urea cycle, nitrogen released by the catabolism of amino acids is converted to urea. The urea cycle also plays a role in biosynthesis of amino acids. 

Urea is synthesized from the ammonia derived from protein, polypeptide, and amino acid catabolism. Consequently, the amount of urea in the blood is partly determined by protein and amino acid metabolism. Therefore, in considering urea production, the source of the ammonia and the biosynthesis of urea must be discussed. The ammonia is derived mainly from amino acid breakdown. In liver, the amino acid pool is derived from the breakdown products of ingested and endogenous proteins and from amino acids synthesized de novo. 

The amount of an enzyme present in a cell at any given time depends on the balance between the rate of its synthesis and breakdown. Different enzymes have very different half-lives ranging from a few minutes to several days (page 286). Those with short half-lives are inducible and repressible, i.e. their rates of synthesis and/or breakdown, and hence the level in the cell, are readily altered in response to environmental factors. Some enzymes are very sensitive to the nutritional state. Thus, many of those concerned with amino acid breakdown are afrected by the supply of amino acids as well as by hormonal factors. The changes are particularly large in the case of the aminotransferases that are responsible for the deamination of the essential amino acids. These enzymes virtually disappear when the protein intake is very low so that the essential amino acids are effectively conserved. The enzymes of the urea cycle are also significantly reduced. 

A. Proteolytic Enzymes. B. Amino Acid Dehydrogenases and Transaminases. C. Amino Acid Activating Enzymes. D. Other Enzymes of Amino. Acid Breakdown and Synthesis. E. Enzymes of Sulfur Metabolism. 

The products of amino acid oxidase activity have no effect on blood pressure. In the alternative pathway for the amino acid breakdown by renal tissue, amino acid decarboxylases convert amino acids to the corresponding amines, some of which are powerful pressor substances. 

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