Difference between histidine and histamine in the mechanistic pathway of the fluorescence reaction with ortho-phthalaldehyde.
Histamine reacts with ortho-phthalaldehyde (OPA) in an alkaline medium to form an unstable fluorescent adduct (Fbase-Hm). Acidification of the solution to pH 2-4 gives a stable and highly fluorescent adduct (Facid-Hm). In contrast, histidine develops a relatively stable fluorescent adduct (Fbase-Hd) with OPA in an alkaline medium. Upon acidification of the solution, however, only trace amounts of the alternative fluorescent adduct (Facid-Hd) are produced although Fbase-Hd disappears similarly to Fbase-Hm. In this paper, the reaction pathway of histidine with OPA was clarified by the kinetic analysis of formation and degradation of Fbase-Hd. In comparing the results of this study with the previous ones for histamine (T. Yoshimura et al., 1987, Anal. Biochem., 164, 132-137), we elucidate the difference between histamine and histidine in the mechanism of fluorescence reaction with OPA. The presence of the carboxyl group in histidine not only stabilizes Fbase-Hd in an alkaline medium but also prevents the formation of a 1:2 adduct of histidine and OPA, the precursor of Facid-Hd.
Yoshimura
T
T
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Kamataki
T
T
Miura
T
T
D055598:Chemical Phenomena; D002621:Chemistry; D005453:Fluorescence; D006632:Histamine / Q000032:analysis*; D006639:Histidine / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009764:o-Phthalaldehyde
D006639:Histidine; D009764:o-Phthalaldehyde; D006632:Histamine