Amino adds essential

Of the 20 common amino adds, ten are essential in the sense that they are required by humans for protein construction and cannot be synthesized in the body. These are designated by an asterisk in Table 23.3. Clearly the proteins we eat should contain these essential amino adds. Beyond that, a high-quality protein contains the various amino adds in the... 

All living spedes are able to synthesise amino adds. Many spedes, however, are defident in their ability to synthesise within their own metabolic system all the amino acids necessary for life. The eight amino acids with this spedal significance for file human species are called essential amino adds, these are ... 

Name five of the eight essential amino adds. 

The eight essential amino adds are listed immediately after Table 8.2. 

Arginine An essential amino add that is physiologically active in the L-form. [NIH]... 

The 10 amino adds listed in Table 1-8-1 cannot be synthesized in humans and therefore must be provided from dietary sources. These are called the essential amino adds. Arginine is required only during periods of growth, or positive nitrogen balance. 

The four-step synthesis of a, -diaminocaprolactam shown in Figure 5.29 is part ofa chemoenzymatic route to (S)-lysine, an essential amino add in our diet [135], The racemic caprolactam (azepan-2-one) product is then hydrolyzed selectively to (S)-lysine, using an immobilized (S)-hydrolase enzyme. 

To illustrate a few aspects of amino add production by enzymatic methods, ffie production of L-phenylalanine will be considered in some detail. L-Phenylalanine is important as an essential amino add for human nutrition and is used as an intermediate for the synthesis of the artifidal sweetener, aspartame. Other examples of the industrial production of amino adds by enzymatic methods are described briefly in Appendix 2. 

The essential amino adds (histidine, isoleudne, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) are required in the diet. Arginine and increased amounts of histidine are required dining periods of growth. 

Tyrosine is produced by hydroxylation of the essential amino add phenylalanine. 

Regulation of the dietary intake of amino acids can also be important when considering the treatment of certain defects in amino add biosynthesis. Phenylalanine is an essential amino acid that is also used to generate the nonessential amino add tyrosine. The enzyme that carries out this readion is the mixed function oxidase phenylalanine hydroxylase (PAH). Inherited deficiencies in PAH are associated with a condition known as phenylketonuria (PKU see Case 38). The absence of PAH results in elevations of phenylalanine and various phenylketones, the accumulation of which is associated with the neurologic defects seen in this disorder. PKU can be treated by controlling the dietary intake of phenylalanine. Diets low in phenylalanine will help prevent excessive elevations in phenylalanine. Phenylalanine can not be completely eliminated from the diet because it is an essential amino acid needed for protein synthesis. In the absence of PAH activity, tyrosine becomes an essential amino add because it cannot be generated from phenylalanine. 

Phenylalanine is an essential amino add that is also used to generate the nonessential amino acid tyrosine. 

Organisms other than plants vary widely in their capacity to synthesize amino acids from metabolic intermediates and fixed nitrogen. For example, many microorganisms can produce all the amino acids they need. In contrast, animals can synthesize only about half the amino acids they require. The nonessential amino acids (NAA) are synthesized from readily available metabolites. The amino acids that must be provided in the diet to ensure proper nitrogen balance and adequate growth are referred to as essential amino adds (EAA). 

Various sugars make the listings, denoted by the suffix -ose. Various amino acids also make the listings, denoted by the suffix -ine, notable examples being L-alanine and L-phenylalanine, commonly associated with nutritional supplements. Arginine, an essential amino add (not manufactured in the body), is said to be an inhibitor. The suffix pyridoxal is fisted as an inhibitor, whereby it may be noted that pyridoxine (or pyridoxin) is called vitamin B6. 

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