Amino acids destruction

For glutamic acid (18) and glycine (10) the yield of ammonia varies approximately as the cube root of the concentration. This variation agrees with the diffusion of the spur model which derives from the hypothesis that at higher solute concentrations, water radicals are scavenged which would react with each other in more dilute solution. However, for the effect of cathode rays on the aromatic amino acids phenylalanine, tryptophan, and tyrosine and for cystine, this relationship is inverted, and amino acid destruction decreased with an increase in concentration (29). 

The proportion of reactions in the side chain, relative to those at the a-carbon atom, increases with the size of the side chain. In amino acids with a reactive side chain, such as the aromatic and sulfur-containing amino acids, this proportion is increased further. Similar trends are found in the data for amino acid destruction. Thus, Shimazu and Tappel (34) found that at pH 7 in 0.01M solution the most radiolabile among the amino acids studied were phenylalanine and methionine. They also showed an increase in radiolability with the size of the side chain for aliphatic amino acids. In comparing the radiolabilities of the amino acids, it should be borne in mind that pH and concentration effects vary from one amino acid to another. 

Automatic amino acid analysis of polyamino acids irradiated in 0.1% oxygen-free aqueous solution showed that for PGA, PDLA, and poly-L-proline, amino acid destruction increased linearly with dose up to 1 Mrad. The 6-values from these analyses were G(-Glu) = 0.85, G(-Ala) = 1.9, G(-Pro) = 1.8. 

The presence of O2 during irradiation of PDLA (0.1% solution, 1 atm. O2), increased the amino acid destruction G = —1.9 in N2 and 2.1 in O2) and the formation of amide-like ammonia (G = 0.66 in N2, 2.0 in O2). The acidic amino acid formed in N2 was not found in samples irradiated in O2, but the amount of aspartic acid was increased. It is possible that O2 converted the precursor of the unknown acidic amino acid into aspartic acid. The small amount of glycine apparently was not affected. 

Amino Acid Destruction in Beef by High Energy Electron Beam Irradiation... 

Electron beam and 7-ray irradiation of ground beef have been compared with regard to amino acid destruction. The most sensitive acid to irradiation was cystine, followed by tryptophan and histidine. The greatest amounts of destruction were obtained with 24 m.e.v., 200 juamps electron beam irradiation. Electron beam density appeared to be as important as total irradiation dose in destroying amino acids. In general, little damage to amino acids and thus to the nutritive value of beef was produced by irradiation. 

In a study on model systems prepared from single amino acid and glucose in molar ratio 2 1, approximating the composition of shell-free cocoa beans, Rohan and Stewart (52) reported that amino acid destruction from heating was temperature dependent and practically ceased after one hour. Sugar destruction contintued at a rate dependent on reaction temperature until the end of the experiment (Table IX). 

Proteins have been hydrolyzed by treatment with sulfuric acid, hydrochloric acid, barium hydroxide, proteolytic enzymes, and other hydrolytic reagents, but no condition has been found which avoids some destruction or incomplete liberation of tryptophan, cystine, and some other amino acids. The early work on this problem has been reviewed by Mitchell and Hamilton (194). The literature and their own excellent experiments on the hydrolysis problem in relation to the liberation and destruction of tryptophan have been presented recently by Spies and Chambers (269). 

Lesions in conjunction with concentration studies can also be useful. Section of dorsal roots and degeneration of afferent fibres produces a reduction in glutamate and substance P which can then be associated with sensory inputs. Temporary reduction of the blood supply to the cord causes preferential destruction of interneurons and a greater loss of asparate and glycine, compared with other amino acids and so links... 

Pseudomonas has been disclosed [233], The method consists of mutating the genes by UV irradiation or other methods and separating the desired protein. A specific amino acid sequence, present in that protein, shows the function for regulating the expression of benzothiophene oxidase gene. The fact that the protein is thought to be useful for both, desulfurization and for purification of sulfur contaminated soil or waste waters indicates a probable destructive pathway. 

Detection and quantification of protein by measuring absorbency at 280 nm is perhaps the simplest such method. This approach is based on the fact that the side chains of the amino acids tyrosine and tryptophan absorb at this wavelength. The method is popular, as it is fast, easy to perform and is non-destructive to the sample. However, it is a relatively insensitive technique, and identical concentrations of different proteins will yield different absorbance values if their content of tyrosine and tryptophan vary to any significant extent. Hence, this method is rarely used to determine the protein concentration of the final product, but it is routinely used during downstream processing to detect protein elution off chromatographic columns, and hence track the purification process. 

The method of protein hydrolysis was important acid hydrolysis caused destruction of tryptophan but alkaline treatment gave even greater losses of other amino acids especially cystine. The amino acids were usually separated by then standard chemical procedures based on differences in solubility, selective precipitation by agents such as Reinecke salt (proline and hydroxyproline), or flavianic acid (arginine). 

Although the ubiquitination site(s) of -catenin was previously unknown, two lysines of I/cBa located ten and nine residues upstream of the destruction motif had been shown to be necessary and sufficient for ubiquitination and degradation [18, 19]. By analogy, a jS-catenin lysine (Lysl9) 13 residues upstream of the destruction motif was predicted to be the site where / -catenin is ubiquitinated. This was confirmed by the in vitro ubiquitination assay, in which a 26-amino acid j8-catenin peptide that contains Lysl9 and the doubly phosphorylated destruction motif was ubiquitinated in an -dependent manner to an overall level comparable to an... 

---