Influences of metal ions on the reaction of amino and imino acids with fluorogenic reagents

Abstract When a twofold excess of metal ions (Cu 2+ , Ni 2+ , Zn 2+ , Mg 2+ , Ca 2+ , Fe 3+ , and Al 3+ ) was added to a reaction medium of amino acids (1–50 μ m each) with the fluorogenic reagents NBD-F (4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole), DNS-Cl (5- N,N -dimethylaminonaphthalenesulfonyl chloride), OPA ( o -phthalaldehyde), and fluorescamine (4-phenylspiro[furan-2(3 H ), 1′-phthalan]-3,3′-dione), a reduction of derivatization was observed. The effect was especially marked on the reaction with NBD-F. The derivatization of His and Asp with DNS-Cl and fluorescamine and of His with OPA was suppressed by Cu 2+ and/or Ni 2+ . The suppression by the metal ions can be overcome by the addition of EDTA to the reaction medium. For determination of a small amount of amino and imino acids (less than μ m ) the addition of a chelating reagent to biological samples is recommended before derivatization with these electrophilic reagents.