Abstract
Abstract Amino acid esters and amides fail to produce strong fluorescence following their reaction with o-phthalaldehyde (OPA) in the presence of β-mercaptoethanol. The lack of luminescence appears to arise from a quenching phenomenon rather than from reduced reactivity of these substrates toward OPA. The amido hydrogen in the peptide linkage has been implicated in the loss in fluorescence yield. o-Phthalaldehyde (OPA) has proven to be a very useful reagent for converting amino acids to fluorescent isoindole derivatives1. This derivatization process permits the visualization of femtomolar quantities of amino acids. Unfortunately, this technique has not been applied successfully to the derivatization of peptides2,3, except for those containing lysine residues, in which the terminal amino group is attacked by the reagent4. It is the purpose of this note to more clearly define the limitations of OPA as a fluorogenic reagents for peptides and amino acid esters.
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