Dinitrophenyl peptides, identification

In a few cases, alkaline hydrolysis has proved applicable to special problems. Tryptophan is not destroyed in alkali, and analysis of alkaline hydrolyzates forms the basis of one method for quantitative determination of this amino acid (e.g., Dreze, 1960). Despite the fact that tryptophan-containing peptides should be more stable in alkali than acid, partial alkaline hydrolysis has not been employed for identification of this type of peptide. Amino acids often can be regenerated by alkaline hydrolysis from derivatives obtained by the amino-terminal end-group methods. Dinitrophenyl amino acids and phenylthiohydantoin (Fraenkel-Conrat et al., 1955) as well as hydantoin (Stark and Smyth, 1963) derivatives of amino acids can be treated in this manner. 

Peptide analysis. The reagent was introduced by Sanger for identification of the amino-terminal group of a protein or peptide. Condensation occurs under mild conditions to form a 2,4-dinitrophenyl protein on acid hydrolysis the terminal... 

The sequencing methods and determination of C-terminal and N-terminal amino acids are now widely used in biochemical research. The identification and quantitation of the characteristic degradation products can be accomplished by the gas-phase analytical methods. Thus, GC of both dinitrophenyl and various hydantoin amino acid derivatives has now been widely documented. Separation of thiohydantoins [244,245], phenylthiohydantoins [490,491] and methylthiohydantoins [492] generally requires additional silylation for the sake of volatility. Furthermore, acyl derivatives of similar substances have also been reported [493,494]. The most obvious advantage of GC for determination of the Edman degradation products is sensitivity which is particularly important in the sequence analysis of only minute amounts of proteins and peptide hormones. 

The identification of N-terminal amino acids in peptides and proteins is of considerable practical importance because it constitutes an essential step in the process of sequential analysis of peptide structures. Many N-amino acid derivatives have been proposed for this purpose and the ones most commonly studied by TLC are 2,4-dinitrophenyl (DNP)-and 5-dimethylaminonaphthalene-l-sulfonyl (dansyl, Dns)-amino acids, and 3-phenyl-2-thiohydantoins (PTH-amino acids). Recently, 4-(dimethylamino)azobenzaie-4/-isothio-cyanate (DABITC) and phenyl-isothiocyanate (PITC) have also been investigated as derivatizing agents of amino acids. 

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