Protein hydrolysis alkaline

The iodoacetyl group of both isomers reacts with sulfhydryls under slightly alkaline conditions to yield stable thioether linkages (Figure 9.7). They do not react with unreduced disulfides in cystine residues or with oxidized glutathione (Gorman et al., 1987). The thioether bonds will be hydrolyzed under conditions necessary for complete protein hydrolysis prior to amino acid analysis. 

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). 

Fischer then synthesized a number of di-and tripeptides and showed that their properties were identical to those of the di-and tripeptides which could be obtained after partial protein hydrolysis. A peptide containing 18 amino acid residues was eventually synthesized. Molecules containing peptide bonds were found to give a characteristic pink to purple color in the presence of dilute alkaline copper sulfate. The simplest compound which does this is biuret, formed when urea is heated at 150-160 °C ... 

Alkaline Proteases —derived from bacteria. They lind wide application in delergents. leather tanning, protein hydrolysis, brewing, and silver recovery from film. 

Protein hydrolysis Water activity Water content Water retention alkaline, 437 enzymatic of p-glucan, 753 olive oil substrate, 373 polysaccharides characteristics of, 728-729 sulfuric acid, 724-727 trifluoroacetic acid (TFA), 721-726, 729-730... 

Hydrolysis. Two types of hydrolytic reactions occur in proteins at alkaline pH. These are the hydrolysis of peptide and amide bonds and the hydrolysis of arginine to ornithine. Amide bonds are hydrolyzed rapidly in alkaline solution probably as shown in Equation 4 (21). 

Selective alkylation of amino groups can be achieved by exposure of proteins, in alkaline solution, to low concentrations of formaldehyde and sodium borohydride. Both a- and e-amino groups are modified. e-N-Methyllysine, an e-N,N-dimethyllysine, may be readily quantitated after acid hydrolysis (see 2.12.1.2). The physical properties of the alkylated protein derivatives are very similar to those of the un-... 

Protein hydrolysis during laundry wash Alkaline protease... 

There are numerous protocols for protein hydrolysis, involving minor variants of the standard procedure, that are intended to minimise the destruction of particular amino acids (tryptophan and cysteine/cystine in particular) through the sensitivity of their side-chains to the reaction conditions, especially when access of oxygen is not prevented. Tryptophan largely survives alkaline hydrolysis (but other coded amino acids, particularly serine and threonine, but also arginine and cysteine, do not). 

Blood, plasma Protein adducts Protein precipitation, alkaline hydrolysis. Negative ion CI GC-MS 25 nM plasma exposure Capacio et al. (2004)... 

It had been noted early on that proteins could be cleaved by acid or alkaline hydrolysis, yielding what was later called amino acids. Leucine was the first amino acid isolated after protein hydrolysis (1819) followed in 1820 by the simplest of all amino acids, glycine. A number of more or less brutal methods were used for the degradation of proteins but it was soon realized that acid hydrolysis was the least damaging to the desired end-products, the amino acids. In 1846 Liebig obtained crystals of the first aromatic amino acid, tyrosine. At the end of the 19th century, a dozen amino acids had been isolated in pure form, but the list of 20 standard amino acids in protein was not completed until 1936 when threonine was discovered. 

Since lysinoalanine is so readily formed by the treatment of protein with base, ornithinoalanine (Figure 7) also should be found in the hydrolysates of alkali-treated proteins, if only ornithine were a constituent amino acid of proteins. Ornithinoalanine may indeed become such a constituent amino acid of proteins. The alkaline conditions to which proteins are exposed provide the base catalysis required for the hydrolysis of the guanido group of arginine (Figure 8) and the formation of ornithine. The presence of ornithine in alkali-treated proteins was shown... 

The product of the addition reaction, lysinoalanine, has been observed on numerous occasions of treatment of proteins under alkaline conditions (7,8,13,14,15). The amino acid is stable to the conditions of total protein hydrolysis and is easily accounted for in amino acid analysis. A segment of the chromatogram showing lysinoalanine found in the sample from a canned food product for human consumption is shown in Figure 15. 

Succinimidyl esters are an excellent first choice to activate amine-reactive probes, but their low solubility has led to the alternative use of sulphonyl chlorides (Figure 4.17). The resultant sulphonamide link is extremely stable, even more stable than an amide link, and will survive even complete protein hydrolysis - a property that can be exploited in protein analysis. The disadvantage of sulphonyl chlorides is that they are unstable in aqueous buffers under mildly alkaline conditions (typically the pH required for the reaction with aliphatic amine ). Hence extreme care must be taken to perform bioconjugations with sulphonyl chlorides at low temperatures (approx 4 °C). Alternatively, amine-reactive probes may be equipped with isothiocyanate traps , from which thiourea links are formed post-reaction with amine functional groups, or with aldehydes, from which Schiff sbase links can be formed with amine functional groups (Figure 4.17). 

The sugar content of the hemicellulosic powder increases with the rise in alkalinity and the decrease in straw content. The first can be explained by a more efficient action of NaOH on bran before coextrusion, which favours the release of more hemicelluloses, and by an increase of protein hydrolysis at high soda content. In fact, the rise in the sugar content is correlated with the decrease in the proteic material (data not shown). The second aspect is linked to the extraction of lignin from straws by soda, which is known to be very efficient in... 

As has been stated, tryptophan is completely destroyed by acid hydrolysis. Some methods protect tryptophan with compounds such as 2-mercaptoethanol, but these methods do not always give reproducible results. Other methods for the liberation of tryptophan have included proteolysis by enzymes. An early method developed by Spies and Chambers (1949) did not require freed tryptophan. It is a colorimetric assay, reacting the tryptophan with p-dimethylaminobenzaldehyde (PDBA). This method has been useful in pure proteins, but many food matrices have interfering substances. In addition, tryptophan is one of only two amino acids with a strong extinction coefficient in a usable ultraviolet (UV) range (approximately 280 nm depending on solvent, etc.). However, the most reliable method of tryptophan analysis is to release the amino acid from protein with alkaline hydrolysis (Lucas et al., 1980) and then use chromatography for quantification. 

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

Fig. 15. En2ymatic hydrolysis of wheat gluten at 72.5°C and pH 7.5 by an alkaline protease from Bacillus licheniformis. The numbers on the curves are en2yme—substrate ratios (E/S) in activity units (AU)/kg of protein where S = 7.4% (N x 5.7).

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