REACTIVITY OF PYRROLE PIGMENTS .13. IDENTIFICATION OF THE REACTION-PRODUCT GENERATED FROM BILE-PIGMENTS BY THE SUPEROXIDE ANION

The UV/Vis spectra of the conjugated bases (NH deprotonation) of biliverdin IX α (BV), mesobiliverdin IX α (MBV), biliverdin IX α dimethyl ester (BV -DME) and mesobiliverdin IX α dimethyl ester (MBV - DME) are shown. They resemble those obtained for the reaction products of these biliverdins with superoxide anion ( {Mathematical expression}). These results confirm that the bile pigments react with {Mathematical expression} giving the lactam NH deprotonated conjugated bases and inducing {Mathematical expression} dismutation. The spectrometric titrations of BV, MBV and their dimehyl esters show that the lactam NH of the vinyl substituted biliverdins is more acidic (ΔpKa{cross ratio}0.5). The spectra of the lactam NH bisdeprotonated conjugated bases of the bilatrienes-abc studied (BV4- and MBV4-) can be obtained in DMSO/H2O/OH- systems of high basicity function (H-{cross ratio}23). Because of the low oxidation potentials of BV3- and of the corresponding trianion of bilirubin IX α (studied by voltammetry) an alternative metabolic degradative pathway is suggested for bilirubin, involving the interaction in lipophilic media with {Mathematical expression} and oxidation of the conjugated base generated by NH deprotonation. © 1990 Springer-Verlag.