Hydrolysis, of proteins

Products of the Hydrolysis of Proteins.—(a) Metaproteins.—In a test-tube place 10 cc. of the egg-white solution and 1 cc. of a 10 per cent solution of sodium hydroxide. In a second tube place 10 cc. of the egg-white solution and 1 cc. of concentrated hydrochloric acid. Place the tubes in a beaker containing about 300 cc. of water at 50°, and allow them to stand from 15 to 20 minutes. The temperatures should not fall below 40°. The protein is partly converted into alkali-albumin and into acid-albumin. 

Boil 2 cc. of the solution in each tube. Is protein precipitated Add to 2 cc. of the alkali albumin a drop of dilute hydrochloric acid. Is the precipitate soluble in dilute alkali Add to 2 cc. of the alkali albumin a drop of dilute hydrochloric acid heat to boiling. Is the precipitate soluble in dilute alkali as before Explain. Add to 2 cc. of the acid albumin a drop of dilute alkali. Is the precipitate soluble in dilute acetic acid Add to 2 cc. of the solution of alkali albumin an equal volume of a saturated ammonium sulphate solution. Is the protein precipitated  

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X-alanine, 2-aminopropanoic acid, C3H7NO2, CH3.CH(NH2)C00H. M.p. 297X. One of the amino-acids obtained by the hydrolysis of proteins. 

C4H6N2O2. Sublimes 260"C sparingly soluble in water hydrolysed by alkalis or mineral acids to glycylglycine. It and substituted dike-topiperazines are formed by the condensation of amino-acids, and are obtained in small quantities on the hydrolysis of proteins. 

The above method, due to Sorensen, is of great importance in following the course of hydrolysis of proteins by enzymes (p. 516). For example, if the protein and its hydrolysis are represented thus ... 

Chymotrypsin (Section 27 10) A digestive enzyme that cat alyzes the hydrolysis of proteins Chymotrypsin selectively catalyzes the cleavage of the peptide bond between the car boxyl group of phenylalanine tyrosine or tryptophan and some other ammo acid... 

Hydroxylated amino acids (eg, 4-hydroxyproline, 5-hydroxylysine) and A/-methylated amino acids (eg, /V-methylhistidine) are obtained by the acid hydrolysis of proteins. y-Carboxyglutamic acid occurs as a component of some sections of protein molecules it decarboxylates spontaneously to L-glutamate at low pH. These examples are formed upon the nontranslational modification of protein and are often called secondary protein amino acids... 

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). 

Protein Hydrolysis. Acid hydrolysis of protein by 6 MHQ in a sealed tube is generally used (110°C, 24-h). During hydrolysis, slight decomposition takes place in serine (ca 10%) and threonine (ca 5%). Cystine and tryptophan in protein cannot be deterruined by this method because of complete decomposition. 

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. 

Currently, a-amino acids are prepared by several routes such as by the fermentation of glucose, by enzyme action on several substances and by the hydrolysis of proteins. Many methods for synthesising the polymers are known, of which the polymerisation of A -carboxyanhydrides is of particular interest, as it yield-products of high molecular weight (Figure 18.24). 

The most recent advance in treating HIV infections has been to simultaneously attack the virus on a second front using a protease inhibitor. Recall from Section 27.10 that proteases are enzymes that catalyze the hydrolysis of proteins at specific points. When HIV uses a cell s DNA to synthesize its own proteins, the initial product is a long polypeptide that contains several different proteins joined together. To be useful, the individual proteins must be separated from the aggregate by protease-catalyzed hydrolysis of peptide bonds. Protease inhibitors prevent this hydrolysis and, in combination with reverse transcriptase inhibitors, slow the reproduction of HIV. Dramatic reductions in the viral load in HIV-infected patients have been achieved with this approach. 

In addition, our results suggest that removal of hpids improves both yield characteristics and elemental characteristics. Recent work by Liden et al. (1995) suggests that the methanol-chloroform method used here is more effective than other methods, such as treatment with NaOH solution, or the maintenance of an acidic environment and ultrafiltration of products during collagen extraction. It is speculated that the presence of hpids in archaeological bone samples may interfere with the acid hydrolysis of protein during... 

Proteolysis The hydrolysis of proteins, usually by enzyme action, into simpler substances. 

YS Kim. Intestinal mucosal hydrolysis of proteins and peptides in peptide transport, and hydrolysis. A Ciba Foundation Symposium. Exerpta Medica. Amsterdam ... 

Before measuring the mass spectra, it is appropriate to concentrate and refine the peptides that are released into the solution by trypsin-catalysed hydrolysis of proteins. The reverse phase Cig in the 10 pi tip of the automatic pipette (commercially available ZIP-TIP, Millipore Corporation, Bedford, MA, USA) was used. The peptides that are rather... 

L. Hill, Hydrolysis of Proteins, Advances in Protein Chemistry, 20, 37 (1965). 

Although zinc, cadmium, and mercury are not members of the so-called main-group elements, their behavior is very similar because of their having complete d orbitals that are not normally used in bonding. By having the filled s orbital outside the closed d shell, they resemble the group IIA elements. Zinc is an essential trace element that plays a role in the function of carboxypeptidase A and carbonic anhydrase enzymes. The first of these enzymes is a catalyst for the hydrolysis of proteins, whereas the second is a catalyst for the equilibrium involving carbon dioxide and carbonate,... 

In some cases, the forms in which the organic materials are present are not easily separated or identified. Some chemical pretreatment is necessary before the analytical procedures can be used. These pretreatments may include the preparation of volatile derivatives for use in gas chromatography, or the splitting of a large and otherwise intractable molecule, as in the hydrolysis of proteins to their constituent amino acids. 

Simply on the basis of the normal composition of marine organisms, we would expect proteins and peptides to be normal constituents of the dissolved organic carbon in seawater. While free amino acids might be expected as products of enzymic hydrolysis of proteins, the rapid uptake of these compounds by bacteria would lead us to expect that free amino acids would normally constitute a minor part of the dissolved organic pool. This is precisely what we do find the concentration of free amino acids seldom exceeds 150 xg/l in the open ocean. It would be expected that the concentration of combined amino acids would be many times as great. There have been relatively few measurements of proteins and peptides, and most of the measurements were obtained by measuring the free amino acids before and after a hydrolysis step. Representative methods of this type have been described [245-259]. Since these methods are basically free amino acid methods, they will be discussed next in conjunction with those methods. 

See Section IV.1 for alternative methods of chiral resolution. Partial chemical hydrolysis of proteins and peptides with hot 6 M HC1, followed by enzymatic hydrolysis with pronase, leucine aminopeptidase and peptidyl D-amino acid hydrolase, avoids racemiza-tion of the amino acids281. The problems arising from optical rotation measurements of chiral purity were reviewed. Important considerations are the nonideal dependence of optical rotation on concentration and the effect of chiral impurities282. 

Borsook s review article (1952) is a good starting point for a consideration of changes in thought which have occurred with regard to biosynthesis of protein. .. the possibility that synthesis could occur by reverse of hydrolysis of proteins. .. is discussed (and disagreed with) and so is protein synthesis by transpeptidation. Both theories were current at the time. .. Borsook needs only half a page to discuss the role of nucleic units in protein synthesis. 

This enzyme catalyzes the hydrolysis of proteins, including elastin, with preferential cleavage at Ala-Xaa. The following are reviews on the molecular and physical properties of this enzyme [EC 3.4.21.36 (pancreatic) and EC 3.4.21.37 (leukocyte)]. 

This aspartic proteinase [EC 3.4.23.22], from the ascomy-cete Endothia parasitica, catalyzes the hydrolysis of proteins with broad specificity similar to that of pepsin A, with preferential action on substrates containing hydrophobic residues at PI and PI. ... 

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