Induction of Wavelength-Dependent Photochemistry in Bilirubins by Serum Albumin |
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Authors: | Antony F McDonagh Giovanni Agati David A Lightner |
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Institution: | (1) Division of Gastroenterology, Box 0538, S-357, University of California, San Francisco, CA 94143-0538, USA, US;(2) Istituto di Elettronica Quantistica, CNR, Sezione INFM di Firenze, I-50127 Firenze, Italy, IT;(3) Department of Chemistry, University of Nevada, Reno, NV 89557-0020, USA, US |
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Abstract: | Summary. Quantum yields for Z⇄E photoisomerization of the natural bi-chromophore bilirubin IXα in ammoniacal methanol solution were found to vary with excitation
wavelength, whereas no variation (within experimental error) was observed for xanthobilirubic acid and for symmetrically substituted
bilirubins (bilirubin IIIα, bilirubin XIIIα, and mesobilirubin XIIIα) in the same solvent. The quantum yield for Z⇄E photoisomerization of xanthobilirubic acid bound to human serum albumin was also invariant with excitation wavelength. In
contrast, quantum yields for Z⇄E photoisomerization of the symmetrically-substituted bilirubins did show marked excitation wavelength dependency when they
were bound to human serum albumin. These results show that quantum yields for Z⇄E photoisomerization of bilirubins are markedly sensitive to protein binding and to the nature of pyrrole ring β-substituents.
They also demonstrate that wavelength-dependent photochemistry is characteristic of bilirubins with non-identical pyrromethenone
chromophores, as expected from exciton coupling theory, and that complexation with albumin induces wavelength-dependent photochemistry
in symmetrically substituted bilirubins.
Received January 13, 1998. Accepted January 27, 1998 |
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Keywords: | , ,Bile pigments, Exciton coupling, Human serum albumin, Phototherapy, Pyrromethenone, |
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