Edman has also devised the highly sensitive "dansy1" method...

Edman has also devised the highly sensitive "dansy1" method in which a peptide is treated with 5 -dimethy1aminonaphthalenesulfony1 chloride, followed by acidic hydrolysis. A derivative of the N-terminal residue is obtained which can be followed during its analysis by virtue of its characteristic fluorescence. What is the derivative? Why does it survive the acid treatment that cleaves the peptide bonds?

Key Concepts

Fluorescent Labeling

Fluorescent labeling is a technique in which molecules are tagged with fluorescent compounds, allowing for sensitive detection and analysis. When applied to peptides, labeling the N-terminal residue makes it possible to track and quantify the molecule during separation and detection processes due to the unique fluorescence emission of the label.

N-Terminal Derivatization

N-terminal derivatization involves chemically modifying the free amino group of the first amino acid in a peptide. This modification is critical in sequencing techniques because it selectively targets the N-terminal residue, enabling stepwise identification or tracking even when the peptide is subsequently cleaved.

Sulfonamide Bond Formation

Sulfonamide bond formation occurs when a sulfonyl chloride reagent reacts with the amino group of an amino acid to form a sulfonamide linkage. This type of bond is robust and resistant to conditions that normally cleave peptide bonds, which is key when the labeled residue must survive subsequent chemical treatments.

Acid Stability of Sulfonamide Bonds

The acid stability of sulfonamide bonds refers to the resistance of these linkages to hydrolysis under acidic conditions. Unlike peptide bonds, which are readily cleaved in acid, the sulfonamide bond formed during the derivatization process remains intact, allowing the modified N-terminal residue to be isolated and analyzed after acid-mediated peptide bond cleavage.

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