Hydrolysis of Proteins and Peptides

Among the analytical methods presently used for the characterization of natural and synthetic peptides and proteins, the primary value of amino acid analysis is the determination of absolute peptide and protein content in solids and solutions and the quantitation of their amino acid composition and stoichiometry. It involves two steps, i.e. complete hydrolysis of peptides and proteins, followed by photometric determination of the released amino adds. The steps are laborious and time-consuming, and there is a continuous need for improvement of the techniques to increase precision and sensitivity. 

Table 2 Add Hydrolysis of Peptides and Proteins Containing Unstable Amino Add Residues1131417-19 ...

Biological amide hydrolysis, as in the hydrolysis of peptides and proteins, is catalyzed by the proteolytic enzymes. These reactions will be discussed in Chapter 25. 

A Tsugita, T Uchida, HW Mewes, T Ataka. Rapid vapor-phase acid (hydrochloric acid and trifluoroacetic acid) hydrolysis of peptide and protein. J Biochem 102 1593-1597, 1987. 

WG Engelhart. Microwave hydrolysis of peptides and proteins for amino acid analysis. Am Biotech Lab 8(15) 30-35, 1990. 

Hydrolysis of peptides and proteins in the GI tract can occur luminally, at the brash border and intracellularly. Luminal activity from the pancreatic proteases trypsin, chymotrypsin, elastase and carboxypeptidase A is mainly directed against large dietary proteins. The main enzymatic activity against small bioactive peptides is derived from the bmsh border of the enterocyte. Brash border proteases, such as aminopeptidase A and N, diaminopeptidease IV and Zn-stable Asp-Lys peptidase, preferentially cleave oligopeptides of up to 10 ammo acid residues and are particularly effective in the cleavage of tri- and tetra-peptides. 

An extensive study of the catalytic hydrolysis of peptides and proteins by Dowex-SO was conducted by Deathrage and co-wodcers (8-11). They found that, in general, the ion exchange resin is superior as add catalyst to HQ [Eq. (3—1)]. For exanq>le, most dipeptides are hydrolyzed about 100 times faster. Ihis was attributed to binding of protonated free amino groups to the polyanion and concentration of the hydrogen ion at the polymer surface. 

In living cells, proteins account for a major fraction of the cellular C and most of the N. We therefore expect that DON released from living organisms will contain proteins. In addition, the prominent amide resonance in the N-NMR spectrum of HMWDON could be derived from peptides and therefore, it is reasonable to hypothesize that proteins dominate the DON reservoir. Direct quantification of proteins in DOM has proven to be difficult (as seen later), so to test the above hypothesis many studies have focused on identifying and quantifying total hydro-lysable amino acids (THAA) in DOM. Amino acids are released from DOM following hydrolysis of peptides and proteins, and most marine DOM studies have used similar methods of hydrolysis and subsequent quantification (i.e., 6M HCl hydrolysis with variable temperature and hydrolysis times, followed by HPLC... 

The preceding techniques are applicable only for the measurement of the rate of hydrolysis of peptides and proteins, and the methods employed in the sequence analysis of polypeptides are required for identification of the residues which form the susceptible bonds. These methods have been reviewed in detail elsewhere (Moore and Stein, 1956 Anfinsen and Redfield, 1956 Greenstein and Winitz, 1961 Canfield and Anfinsen, 1963) and do not require comment here. 

Hydrolysis of peptides and proteins has been observed to be catalyzed by poly(ethylenesulfonic acid) and poly(p-styrenesulfonic acid) Poly(vinyl-benzyltriethylainmonium hydroxide) has been found to catalyze the alkaline hydrolysis of aliphatic esters ... 

Peptide cleavage, partial hydrolysis of peptides and proteins by chemical ( end group analysis) or enzymatic methods (-> proteolysis) for sequence analysis. Limited peptide cleavage (limited proteolysis) is important for various metabolic processes. 

Peptide hydrolysis, complete hydrolysis of peptides and proteins for amino acid analysis or the production of individual amino acids from the peptide or protein hydrolysate. For this purpose, numerous chemical and enzymatic protocols are known, but none of these procedures alone is fully satisfactory. Besides hydrolysis with 6 M hydrochloric acid at 120 °C for 12 h, or with dilute alkali (2-4 M NaOH) at 100 °C for 4-8 h, mixtures of peptidases can also be used for complete peptide hydrolysis. Restricted or limited peptide hydrolysis ( peptide cleavage) is important for - sequence analysis and peptide mapping. 

Peptidases Enzymes that catalyze the hydrolysis of peptides and proteins. 

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