Terminal amino acid analysis

The Edman method of NH2-terminal amino acid analysis. 

Terminal amino acid analysis is performed to identify the nature and homogeneity of the amino- and carboxy-terminal amino acids. If the desired product is found to be heterogeneous with respect to the terminal amino acids, the relative amounts of the variant forms should be determined using an appropriate analytical procedure. The sequence of these terminal amino acids should be compared with the terminal amino acid sequence deduced from the gene sequence of the desired product. 

Peptide analysis, sequencing and synthesis All fluorescent dye labels with reactive groups for amine, dansyl chloride, dabsyl chloride. Fluorescent isothiocyanates. N-Terminal amino acid analysis, peptide sequencing, peptide synthesis, labeling peptides in solution, solid-phase synthesis of labeled peptides 37... 

This reaction forms the basis of one method of terminal residue analysis A peptide is treated with excess hydrazine in order to cleave all the peptide linkages One of the terminal amino acids is cleaved as the free amino acid and identified all the other ammo acid residues are converted to acyl hydrazides Which amino acid is identified by hydrazmolysis the N terminus or the C terminus ... 

Amino acid analysis itself does not directly give the number of residues of each amino acid in a polypeptide, but it does give amounts from which the percentages or ratios of the various amino acids can be obtained (Table 5.2). If the molecular weight and the exact amount of the protein analyzed are known (or the number of amino acid residues per molecule is known), the molar ratios of amino acids in the protein can be calculated. Amino acid analysis provides no information on the order or sequence of amino acid residues in the polypeptide chain. Because the polypeptide chain is unbranched, it has only two ends, an amino-terminal or N-terminal end and a carboxyl-terminal or C-termuial end. 

FIGURE 5.19 N-Tertninal analysis using Edman s reagent, phenylisothiocyanate. Phenylisothiocyanate combines with the N-terminus of a peptide under mildly alkaline conditions to form a phenylthiocarbamoyl substitution. Upon treatment with TFA (trifluo-roacetic acid), this cyclizes to release the N-terminal amino acid residue as a thiazolinone derivative, but the other peptide bonds are not hydrolyzed. Organic extraction and treatment with aqueous acid yield the N-terminal amino acid as a phenylthiohydantoin (PTH) derivative. 

ENZYMATIC ANALYSIS WITH CARBOXYPEPTIDASES. Carboxypeptidases are enzymes that cleave amino acid residues from the C-termini of polypeptides in a successive fashion. Four carboxypeptidases are in general use A, B, C, and Y. Carboxypeptidase A (from bovine pancreas) works well in hydrolyzing the C-terminal peptide bond of all residues except proline, arginine, and lysine. The analogous enzyme from hog pancreas, carboxypeptidase B, is effective only when Arg or Lys are the C-terminal residues. Thus, a mixture of carboxypeptidases A and B liberates any C-terminal amino acid except proline. Carboxypeptidase C from citrus leaves and carboxypeptidase Y from yeast act on any C-terminal residue. Because the nature of the amino acid residue at the end often determines the rate at which it is cleaved and because these enzymes remove residues successively, care must be taken in interpreting results. Carboxypeptidase Y cleavage has been adapted to an automated protocol analogous to that used in Edman sequenators. 

The calculated value for the Hisg-tagged protein is 28,492 Da. N-terminal amino acid sequence analysis (Procise) was carried out on purified recombinant resilin. The following sequence (at 120 pmol yield) was obtained for the first 12 amino acid residues MHHHHHHPEPPV, as expected from DNA sequence analysis. 

Dinitrofluorobenzene (86, X = F) is, because of its reactivity, much used for tagging the NH2 group of terminal amino-acids in protein end group analysis. Once it has reacted with the NH2 it is very difficult to remove again and will thus withstand the subsequent hydrolysis of the protein to its constituent amino-acids. 

Application of the analytical techniques discussed thus far focuses upon detection of proteinaceous impurities. A variety of additional tests are undertaken that focus upon the active substance itself. These tests aim to confirm that the presumed active substance observed by electrophoresis, HPLC, etc. is indeed the active substance, and that its primary sequence (and, to a lesser extent, higher orders of structure) conform to licensed product specification. Tests performed to verify the product identity include amino acid analysis, peptide mapping, N-terminal sequencing and spectrophotometric analyses. 

By use of a crude preparation obtained after the cultivation of Aspergillus niger,104 pectinesterase was purified by repeated chromatography on DEAE-cellulose, using gradient elution. The homogeneity of the product was checked by free electrophoresis, sedimentation analysis, and determination of the N-terminal amino acid (phenylalanine). 

Silk fibroin contains no cystine and the content of lysine and histidine is also low (about 1% in total), but it does contain tyrosine phenolic (13%) and serine alcoholic (16%) sidechains. Since glycine accounts for 44% of the total aminoacid content, an N-terminal glycine residue is reasonably representative of most of the primary amino dyeing sites in silk fibres. Amino acid analysis of hydrolysed reactive-dyed silk indicates that the reaction between fibroin and reactive dyes takes place mainly at the e-amino group of lysine, the imino group of histidine and the N-terminal amino group of the peptide chain. In an alkaline medium, the hydroxy groups of tyrosine and serine also react [114]. 

In 1950 an alternative to the Sanger procedure for identifying N-terminal amino acids was reported by Edman—reaction with phenyl-isothiocyanate to give a phenylthiocarbamide labeled peptide. When this was heated in anhydrous HC1 in nitromethane, phenylthiohy-dantoin was split off, releasing the free a-NH2 group of the amino acid in position 2 in the sequence. While initially the FDNB method was probably the more popular, the quantitative precision which could be obtained by the Edman degradation has been successfully adapted to the automatic analysis of peptides in sequenators. 

Thus, the A-terminal amino acid can be identified by analysis of the thiazolinone, and the process can be repeated on the one-unit-shortened polypeptide chain. Under the acidic conditions, the thiazolinone is actually unstable, and rearranges to a... 

Characterization of Purified Proteins Assessing purity, 182, 555 determining size, molecular weight, and presence of subunits, 182, 566 amino acid analysis, 182, 587 limited N-terminal sequence analysis, 182, 602 peptide mapping, 182, 613 analysis for protein modifications and nonprotein cofactors, 182, 626 protein crystallization, 182, 646. 

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