Chemical oxidative degradation amino acids

In addition to analyzing a protein for characteristics dictated by its specific nature, routine analytical assays are performed namely, amino acid analyses and amino- and carboxy-terminal sequencing. If necessary, disulfide assignments are made. A search is ordinarily conducted for oxidations and/or deamidations. In the case of recombinant proteins particular attention is paid to detecting signal sequences or proteolytically degraded species. In contrast, deletions and chemical modifications can be a consequence of proteins prepared by chemical synthesis. Lastly, tests are applied to determine if the protein is correctly folded into its native three dimensional structure. In addition, with recombinant proteins, sensitive immunological procedures are performed to ensure that host cell proteins have not been copurified with the protein of interest. 

Chemical oxidation reactions and Strecker degradation of amino acids may also result in aldehyde formation (16). These reactions are important for the formation of acetaldehyde in baked or heated Sherries. Chemical oxidation reactions catalyzed by metal ions (Cu, Fe, Mn, Mo) can result in aldehyde production in oak aged distillates (20). Such reactions may also result in the formation of oxidation products from fatty acids released during the secondary fermentation of sparkling wines (21). 

The acetyl CoA that gets on the ferris wheel can be continually replenished through glucose breakdown, or, mainly, through fatty acid degradation (oxidation), or by transformation of certain amino acids. What, however, produces the seats of the ferris wheel, or replenishes them when necessary The seats cannot be replaced by acetyl CoA, which is merely a passenger. The chemicals of the ferris wheel can be restored in part by certain amino acids that can convert to Krebs cycle intermediates. There also is an important side step in which pyruvate can be directly convert to oxaloacetate (D-8). 

Despite the general complexity of DOM, which has been illustrated and discussed at length in this review, several percent of DOM can be attributed directly to lignins, lipids, proteins, and sugars, which are found in freshwaters both as their chemically bound forms and as their free forms. Mostly, these constituents of DOM exist as chemically bound forms, from which their respective monomers (lignin-derived phenols, simple carboxylic acids, amino acids, and monosaccharides) can be liberated by vigorous hydrolytic and/or oxidative degradation. 

Metabolic activation of PAHs consists of an oxidation of the rings of unsubstituted PAHs. These oxidations are carried out by mixed function oxidases of the liver which contain cytochromes P450 and P448 and require reduced nicotine adenine dinucleotide and oxygen. In this oxidation, an epoxide intermediate is formed which has been shown to have the requisite chemical reactivity to bind covalently with DNA and histones and to serve as the ultimate carcinogenic form of PAH. Administration of 3-MC to rats increased hepatic nuclear proteins and caused a turnover of protein of the endoplasmic reticulum. Studies of " C amino acid incorporation showed that 3-MC causes increased protein synthesis and reduced degradation of protein. 

As plant tissues senesce and die, three processes may ensue almost simultaneously. First, enzymes within the dead but sterile and physically intact cells cause proteolysis and other autolytic degradations. The released amino acids, sugars, tannins, phenols, and quinones may be oxidized by chemical or enzymatic catalysis to produce humus-like pigments, or proto-humus as discussed by Stevenson in Chapter 2. This was well illustrated by Cohen (Given and Dickinson, 1975) who observed cellular material of partially polymerized eaco-anthocyanins in residues of Rhizophora mangle deposited in a mangrove swamp in Florida. The autolytic reactions may be prominent in situations where microbial decomposition is slow due to acidity, anaerobiosis, or lack of basic nutrients. 

Other chemical degradation pathways include -elimination, which can lead to racemization and disulphide exchange reactions. The amino acids that may undergo P-elimination include Cys, Ser, Thr, Phe, and Lys (40) and occur especially at alkaline pH (64). The reduction and oxidation of the disulphide bonds are often accompanied by a considerable change in the protein conformation (23,33). An example is the secondary structure of insulin that is disrupted or completely lost when the disulphide bonds are broken (23). The disulphide bond disruption or interchange can also result in an altered three-dimensional structure and therefore a possible loss of activity (40) or aggregation (29). For further details, the reader is directed to the following reviews and book chapters (30,40,62,65). 

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