Amino degradation

Edman degradation (Section 27 13) Method for determining the N terminal amino acid of a peptide or protein It in volves treating the material with phenyl isothiocyanate (CgH5N=C=S) cleaving with acid and then identifying the phenylthiohydantoin (PTH derivative) produced Elastomer (Section 10 11) A synthetic polymer that possesses elasticity... 

Proteins. Proteins (qv) supply amino acids (qv), palatabiHty enhancement, and, when present in more than requited amounts, energy as the proteins are degraded and nitrogen compounds excreted. Dogs and cats can consume and meet amino acid requirements in the form of pure amino acids with complete success. However, animal tissue cannot differentiate between pure, plant, or animal sources of those amino acids, and those amino acids can be obtained much more economically from either plant or animal proteins. 

Enzyme degradation of leaf protein may occur during emshing and separation from the fiber. The amino acids produced by this enzyme action are soluble in the juice and may be lost unless all of the juice is recovered. 

Substitution of alkaline cyanates by isocyanates allows the preparation of 3-substituted hydantoias, both from amino acids (64) and amino nitriles (65). The related reaction between a-amino acids and phenyl isothiocyanate to yield 5-substituted 3-phenyl-2-thiohydantoiQS has been used for the analytical characterization of amino acids, and is the basis of the Edman method for the sequential degradation of peptides with concomitant identification of the /V-terminal amino acid. 

Several enzymes, none of which are completely specific for the enkephalins, are known to cleave Leu- and Met-enkephalin at various peptide bonds. The main enzymes that degrade enkephalin are 2inc metaHopeptidases. The first enkephalin-degrading enzyme to be identified, an aminopeptidase which cleaves the amino terminal Tyr-Gly bond (179), has been shown to be aminopeptidase-N (APN) (180). It is a cytoplasmic enzyme which is uniformly distributed throughout the brain. The increased analgesic activity of synthetic enkephalins substituted by D-amino acids at position 2, eg,... 

Use of D-amino acids in the synthesis of a hairpin loop portion from the CD4 receptor provides a stable CD4 receptor mimic, which blocks experimental allergic encephalomyelitis (144). This synthetic constmct is not simply the mirror image or enantiomer of the CD4 hairpin loop, but rather an aH-D-constmct in the reverse sequence, thus providing stereochemicaHy similar side-chain projections of the now inverted backbone (Fig. 11). This peptide mimetic, unlike its aH-L amino acid counterpart, is resistant to en2yme degradation. As one would expect, the aH-D amino acid CD4 hairpin loop, synthesi2ed in the natural direction, the enantiomer of the natural constmct, is inactive. 

Environmentally, these aLkanolamines present little problem. Only AMP has been studied extensively, but it was found to be degradable, to be of low toxicity to fish and microorganisms, and to be nonaccumulative. TRIS AMINO has been added to water used to ship fish in order to improve viabiUty. 

Strecker Degradation (Oxidative Deamination), Mild oxidizing agents such as aqueous sodium hypochlorite or aqueous A-bromosuccinimide, cause decarboxylation and concurrent deamination of amino acids to give aldehydes. 

Biosynthesis of Protein. The dynamic equilibrium of body protein was confirmed by animal experiments using A/-labeled amino acids in 1939 (104). The human body is maintained by a continuous equilibrium between the biosynthesis of proteins and their degradative metabolism where the nitrogen lost as urea (about 85% of total excreted nitrogen) and other nitrogen compounds is about 12 g/d under ordinary conditions. The details of protein biosynthesis in living cells have been described (2,6) (see also Proteins). 

Cysteine [52-90 ] is a thiol-bearing amino acid which is readily isolated from the hydrolysis of protein. There ate only small amounts of cysteine and its disulfide, cystine, in living tissue (7). Glutathione [70-18-8] contains a mercaptomethyl group, HSCH2, and is a commonly found tripeptide in plants and animals. Coenzyme A [85-61-0] is another naturally occurring thiol that plays a central role in the synthesis and degradation of fatty acids. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

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