Protein partial hydrolysis

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 ... 

An excellent review on protein hydrolysis for amino acid composition analysis has been published by Eountoulakis and Lahm [190], Hydrolysis can be performed by either chemical (under either acidic or basic conditions) or enzymatic means. The acidic hydrolysis itself can be carried out in a liquid or a gas-phase mode. The conventional acid hydrolysis uses 6M HCl for 20-24 h at 110°C under vacuum [200], In these conditions, asparagine and glutamine are completely hydrolyzed to aspartic acid and glutamic acid, respectively. Tryptophan is completely destroyed (particularly in the presence of high concentrations of carbohydrate), while cysteine and sometimes methionine are partially oxidized. Tyrosine, serine, and threonine are partially destroyed or hydrolyzed and correction factors have to be applied for precise quantification [190,201],... 

Enzymatic modification of proteins applicable to foods is reviewed by Whitaker ( ). Described briefly are present uses of proteolytic enzymes for modifying proteins through partial hydrolysis. Major emphasis is placed on those enzymes which bring about aggregation of proteins, cross-link formation, and side chain modification through post-translational changes in the polypeptide chain. 

In any quantitative work on protein hydrolysis, it is necessary to have a measure of the extent of the hydrolytic degradation. The measurement of the number of peptide bonds cleaved during a hydrolytic process is related to the activity of proteinolytic enzymes and the extent of hydrolysis. Various techniques that evaluate the progress of hydrolysis have been reported, such as the trichloroacetic acid (TCA) solubility index, which evaluates the percentage of nitrogen soluble in TCA after partial hydrolysis of the protein. 

The results on the hydrolysis of partially methylated /3-casein by plasmin indicate that proteins radiomethylated to a low level can serve as substrates for trypsin-like enzymes and probably for proteinases in general. Because it is likely that methylation will interfere with enzymatic attack at lysine residues, the complete hydrolysis of /3-casein probably would not be possible. Studies on mastitic milk demonstrate the usefulness of 14C-methyl proteins for qualitative examination of protein hydrolysis in complex multiprotein systems where resolution and characterization of individual protein fragments is difficult. The requirements in such studies are the availability of pure samples of the proteins under investigation and a suitable technique for separating the radio-labeled protein from hydrolytic products. 

Note Depending on the protein source and the degree of hydrolysis, Partially Hydrolyzed Proteins may present an allergenic risk to sensitized individuals. 

These derivatives are not stable to complete acid hydrolysis of proteins, but may be recovered in limited amounts after partial acid hydrolysis. For example, after 90 min of hydrolysis at 100°C in 5.7 N HCl about 30% of the covalently-bound phosphate in phosphoglucomutase was recovered as O-phosphoserine (Milstein 1964), but after 20 hr of hydrolysis at 105°C in 5.7 N HCl, no O-phosphoserine was found (Murray and Milstein 1967). The amount liberated at a certain time will depend on the nature of the residues around the phosphoserine residues in each protein. Hydrolysis of peptides containing O-phosphoserine may often give low yields of serine (e.g. see Nolan et al. 1964). Complete enzymic hydrolysis of proteins or peptides containing O-phosphoserine is the only presently available method for quantitative recovery of this derivative. 

Nucleic acids are vital molecules which carry the genetic code and are responsible for its expression by protein synthesis. The two types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The components of these acids can be obtained by hydrolysis. Partial hydrolysis of a nucleic acid produces nucleotides, which consist of a base, a sugar and a phosphate group. Nucleotides are monomers for nucleic acid polymers, as illustrated in Figure 6.6b. 

Z. Zhou and D. L. Smith, Assignment of disnlfide bonds in proteins by partial acid hydrolysis and mass spectrometry, 7. Protein Chem. 9, 523-532 (1990). 

Any systematic study of cell walls requires an a-D-galacturonanase to release pectic and other matrix components. Molecular structural studies have so far progressed that elaborate models showing the various polymeric constituents in juxtaposition have been generated. After enzymatic elimination of starch and protein, hydrolysis of the residual polysaccharide and estimation of the uronic acids and monosaccharides released furnish considerable information on the composition of agricultural samples. Partial depolymerization affords the complex, well-studied rhamnogalacturonans I and II (RG-I and RG-II). 

Grape proteases are acidic, with an optimum pH near 2.0. In the pH range of must, 40-60% of the potential proteasic activity exists. Protein hydrolysis activity during the pre-fermentation phase varies greatly, depending on grape maturity and harvest treatments. This certainly affects fermentation kinetics but the relationship has never been established. A slight sulfur dioxide additiou (around 25 mg/1), however, has been confirmed to stimulate proteasic activity. This explains, at least partially, its activation effect on fermentation (Section 8.7.3). 

Proteins consist of large numbers of amino-acids joined by the p>eptide link —CO —NH — into chains, as shown in the diagram, where R and R" are amino-acid residues. These chains are called peptides and may be broken into smaller chains by partial hydrolysis (see peptides). Proteins may contain more than one peptide chain thus insulin consists of... 

A critical component of the G-protein effector cascade is the hydrolysis of GTP by the activated a-subunit (GTPase). This provides not only a component of the amplification process of the G-protein cascade (63) but also serves to provide further measures of dmg efficacy. Additionally, the scheme of Figure 10 indicates that the coupling process also depends on the stoichiometry of receptors and G-proteins. A reduction in receptor number should diminish the efficacy of coupling and thus reduce dmg efficacy. This is seen in Figure 11, which indicates that the abiUty of the muscarinic dmg carbachol [51 -83-2] to inhibit cAMP formation and to stimulate inositol triphosphate, IP, formation yields different dose—response curves, and that after receptor removal by irreversible alkylation, carbachol becomes a partial agonist (68). 

In most cases the microspheres were insoluble. The polysaccharides might be partially cross-linked via amido groups formed by the carboxyl groups of the polyanion and the restored free amino group of chitosan. The susceptibility to enzymatic hydrolysis by lysozyme was poor, mainly because lysozyme, a strongly cationic protein, can be inactivated by anionic polysaccharides [207]. 

In mammalian cells, the two most common forms of covalent modification are partial proteolysis and ph osphorylation. Because cells lack the ability to reunite the two portions of a protein produced by hydrolysis of a peptide bond, proteolysis constitutes an irreversible modification. By contrast, phosphorylation is a reversible modification process. The phosphorylation of proteins on seryl, threonyl, or tyrosyl residues, catalyzed by protein kinases, is thermodynamically spontaneous. Equally spontaneous is the hydrolytic removal of these phosphoryl groups by enzymes called protein phosphatases. 

Figure29-1. Partial reactions in the attachment of ubiquitin (UB) to proteins. (1) The terminal COOH of ubiquitin forms a thioester bond with an -SH of E, in a reaction driven by conversion of ATP to AMP and PP. Subsequent hydrolysis of PP by pyrophosphatase ensures that reaction 1 will proceed readily. (2) A thioester exchange reaction transfers activated ubiquitin to Ej. (3) E3 catalyzes transfer of ubiquitin to e-amino groups of lysyl residues of target proteins.

The floss silk from Chorisia speciosa furnished a polysaccharide with a main chain of (1 -> 4) linked P-Xylp substituted at 0-2 by 5 % of uronic acid. The xylan structure also was interposed with a-Rhap units in small amounts. The defatted seeds furnished on aqueous extraction a major fraction, ((9-acetyl, 10 % and protein, 45 %) wich was hydrolysed and analysed by p.c. and GLC, showing Rha (20 %), Ara (16 %), Gal (64 %) and also uronic acids (45 %). Partial hydrolysis gave rise to a polysaccharide free of arabinose, with 46 % of uronic acids. Methylation analysis (GLC -MS) indicated a chain of (1 4) - linked Gal/ (42 % of 2,3,6-Me3-Gal). 

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