Decomposition of proteins

A rate law summarizes the dependence of the rate on concentrations. However, rates also depend on temperature. The qualitative observation is that most reactions go faster as the temperature is raised (Fig. 13.22). An increase of 10°C from room temperature typically doubles the rate of reaction of organic species in solution. That is one reason why we cook foods heating accelerates reactions that lead to the breakdown of cell walls and the decomposition of proteins. We refrigerate foods to slow down the natural chemical reactions that lead to their decomposition. 

From animal tissue, especially bovine lung and liver (e. g. autolysis of comminuted tissue parts, heating with ammonium sulfate in alkaline solution, filtration and acidification yield heparin as complex with protein, removal of fat with alcohol and treatment with trypsine for the purpose of decomposition of proteins, precipitation with alcohol and various purification methods). 

The results obtained with this procedure are similar to those previously reported in the literature by Hangartner, Hagenguth et al and Zeman et al (4, 2, 5, 6). The major exception, being the complete lack of alkylated pyrazines and alkylated thiophenes. These odour-intensive compounds arise from the thermal decomposition of proteins and sulphur containing amino acids. They also develop in the thermally induced reaction of proteins with carbohydrates (Maillard reaction). The authors indicated above have demonstrated that these compounds are invariably produced during the thermal treatment of sludge, a process which is not used in this Authority. 

The first irrefutable observation of a discriminating interaction between enantiomeric surfactants in monolayers was most probably made by Filippus Johannes Zeelen (84) in a detailed study concerning the synthesis, monolayer behavior, and photochemistry of a series of A -stearoylamino acid derivatives that were employed to model the conformation and photochemical decomposition of proteins. Although Zeelen was able to demonstrate significant differences in the force-area curves obtained from racemic and optically active forms of several of these derivatives, publication of this work in 1956 was... 

Two classes of degradation products that are likely to result at least partly from the decomposition of protein hydroperoxides or related peroxyl and alkoxyl radicals have been measured in cells as indicators of the occurrence of oxidative reactions. 

BTR) and "sour" (SOU), increase. Most "bitter" and "sour" flavors are thought to originate from the degradation/decomposition of proteins to bitter and sour flavored peptides and amino acids. 

Meyer-Reil, L.-A., 1981. Enzymatic decomposition of proteins and carbohydrates in marine sediments methodology and field observations during spring. Kieler Meeresforsch., Sonderh., 5 311-317. 

Ammonia was prepared by the alchemists by distilling leather scraps, hoof, horns, and other animal refuse. Because they found that the best ammonia was obtained by distilling deer antlers, the alchemists called ammonia Spirits of Hartshorn. 7 Nature forms ammonia by decomposition of proteins. The odor of ammonia can often be detected around manure piles and other decaying organic matter. 

The free fatty acids formed further oxidize and produce peroxides that decompose into odorous materials. Decomposition of protein-containing materials, particularly if the bacterial count is high, also generates obnoxious smells. This decomposition makes it necessary to follow some or all of the following refining treatments in order to bring the oil to the desired specifications of a final product. To what extent the oils should be refined will depend on its initial quality and on its final use, i.e., cosmetics, pharmaceuticals, or food. 

Skatole.—We have mentioned the fact that indole is important physiologically. Associated with indole in this relationship is the heta-mtXhyX homologue of indole known as skatole. Skatole is the substance to which the characteristic odor of fa ces is due. Both of these compounds are present in faeces and are the result of putrefactive decomposition of protein. 

Tr3Tptophane.—As an intermediate product in the decomposition of proteins we have the amino acid known as tryptophane which may be obtained by the acid hydrolysis of most proteins (p. 389). Tryptophane may be considered either as an indole or skatole derivative. 

About a hundred years ago it was discovered that when any protein is boiled with acid and the resulting solution is allowed to stand, crystals of different substances separate from the solution. Glycine is one of the substances obtained in this way. It is called an amino acid, and it is the simplest of the amino acids obtained by the decomposition of proteins. 

Another amino acid that is obtained by the decomposition of proteins is L-alanine. It is closely similar to glycine in structure, but with one of the hydrogen atoms of glycine replaced by a methyl group, CH3. as shown in the adjacent drawing. 

Decarboxylation of amino acids is a typical feature of the bacterial decomposition of proteins. Both phenylethylamine and tyramine were isolated from putrid meat by Barger and Walpole (30), who considered it extremely probable that they were derived from phenylalanine and tyrosine, respectively. No cell-free preparation of phenylalanine decarboxylase appears to have been reported, but decarboxylation by a crude Streptococcus faecalis preparation provides a valuable method of phenylalanine assay (887). Bacterial tyrosine decarboxylase has been studied in detail (495), especially by Gale and co-workers (summarized in 284). It requires pyridoxal phosphate as coenzyme (26, 326, 327) and, unlike mammalian tyrosine decarboxylase, also attacks dihydroxyphenylalanine. Decarboxylation normally only occurs in acid media and is considered primarily to be a protective mechanism tending to restore the pH to neu-... 

Tryptophan can be converted to indolepyruvic acid either by oxidative deamination or by transamination (e.g., 739, 912) and the indolepyruvic acid can give rise to indoleacetic acid. The fate of indoleacetic acid formed by the bacterial flora of the mammalian gut is discussed below. Bacterial indolelactic acid (e.g., 757) is presumably derived from indolepyruvic acid, but indolelactic acid excreted by mammals (e.g. 17) may be of true mammalian rather than bacterial origin. Indolepropionic acid can also be formed by bacteria (e.g., 412, 633), but further metabolism in mammals of any indolepropionic acid formed in the gut is still obscure (904). Skatole (3-methylindole) has long been known as a product of bacterial decomposition of protein and is formed from tryptophan not only by the bacterial flora of the gut but also in putrefying secretions, e.g., sputum (756). It may well arise by decarboxylation of indoleacetic acid. 

Noskov SY, Lim C. Free energy decomposition of protein-protein interactions. Biophys J 2001 81 737-750. 

During the decomposition of proteins into simpler substances sulphur compounds are released which are reduced to hydrogen sulphide, and nitrogen compounds are reduced to ammonia. CoUoid proteins are transformed into solutions via degradation into peptones, amino acids and finally into ammonia and carbon dioxide. 

From the amino acids, resulting from the decomposition of proteins, ammonia is liberated, and it is oxidized to nitrites and nitrates by nitrifying bacteria Nitrosomonas and Nitrobacter. Denitrifying bacteria produce molecular nitrogen from nitrates. Nitrogen fixation is performed by nitro-genic bacteria (Azotobacter) and cyanobacteria (Nostoc). 

Urea (yoo-REE-uh) is a white crystalline solid or powder with almost no odor and a salty taste. It is a product of the decomposition of proteins in the bodies of terrestrial animals. Urea is produced in the liver and transferred to the kidneys, from which it is excreted in urine. The compound was first identified as a component of urine by French chemist Hilaire Marin Rouelle (1718-1799) in 1773. It was first synthesized accidentally in 1828 by German chemist Friedrich Wohler (1800-1882). The synthesis of urea was one of the most important historical events in the history of chemistry. It was the first time that a scientist had synthesized an organic compound. Prior to Wohler s discovery, scientists believed that organic compounds could be made only by the intervention of some supernatural force. Wohler s discovery showed that organic compounds were subject to the same set of natural laws as were inorganic compounds (compounds for non-living substances). For this reason, Wohler is often called the Father of Organic Chemistry. 

The formation of urea is the evolutionary solution to the problem of what to do with poisonous nitrogen compounds that formed when proteins decompose in the body. Proteins are large, complex compounds that contain relatively large amounts of nitrogen. When they decompose, that nitrogen is converted to ammonia (NH3), a substance that is toxic to animals. If animals are to survive the decomposition of proteins (as happens whenever foods are metabolized), some method must be found to avoid the buildup of ammonia in the body. 

For example, fish excrete the ammonia produced by the decomposition of proteins directly into the watery environment in which they live. Birds, who consume less water by gram of weight than do most other animals, Urea is transported from the liver to the kidneys in the bloodstream. By the time it leaves the body in urine, its concentration is sixty to seventy times its concentration in the bloodstream. 1... 

Problem 16.59. The disagreeable odor of fish is due to methylamine, formed by decomposition of proteins. 

These transformations of amino acid derivatives increases our interest in these compounds prepared by Curtius and his pupils, and gives an impulse to their further study, especially as formaldehyde is such an important compound in the synthesis of sugars by plants, and as the diamino acids and diamines occur as products of decomposition of proteins by enzymes and bacteria, although according to our present knowledge they are not formed in nature in this manner. 

Scheme 8 A proposed model for the LMW-thiol mediated decomposition of protein-bound DNICs. LMW-thiol (e.g., L-Cysteine, glutathione) extrudes the DNIC from the protein-bound DNIC to form LMW-thiol-bound DNIC via thiol ligand exchange. Under anaerobic conditions, both the LMW-thiol-bound DNICs and the protein-bound DNICs are stable, and no DNIC is decomposed. Under aerobic conditions, the LMW-thiol-bound DNIC is rapidly disrupted by oxygen, resulting in eventual decomposition of the protein-bound DNIC [147, 286]...

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