The structure of ?photobilirubin?

Falk, Heinz; Müller, Norbert; Ratzenhofer, M.; Winsauer, K.

doi:10.1007/bf00808942

Cited by 23 publications

(11 citation statements)

References 21 publications

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“…The E,Z and Z,E isomers are the major products formed during anaerobic irradiation of bilirubin IXa-Z,Z with blue light in uitro (10) and are known also as photobilirubins I-A and B (11,12). The E,Z isomer can undergo further photocatalyzed cyclization via the endo vinyl group on the A ring, forming the stable photobilirubin I1 (11)(12)(13).…”

Section: Structural Variations In Bilirubinmentioning

confidence: 99%

Bilirubin Chemistry, Ionization and Solubilization by Bile Salts

Ostrow

Celic

1984

Hepatology

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Bilirubin is a linear tetrapyrrole whose conformation is affected by internal hydrogen bonds formed between the carboxyl side chains and dipyrromethenone rings. Structural variations include: constitutional isomerism of the vinyl or carboxyethyl side chains, geometric isomerism of the methene bridges, tautomerism of the lactam groups, conformational rotations about the central methylene bridge and ionization of one or both carboxyl groups. Aggregation of the dianion into dimers and multimers may occur. The pK,' values of the two carboxyl groups are affected greatly by the environment and may differ widely in micellar solutions like bile. Solubility of bilirubin in water is less than 1 nM at pH = 7 and about 0.1 at pH = 8. Nonetheless, it dissolves poorly in most lipid solvents, except for asymmetrical chloroalkanes. Hydrogen bond-breaking solvents, especially dimethyl sulfoxide, are most effective in solubilizing bilirubin. In bile salt solutions, solubility of bilirubin is well above the concentrations of unconjugated bilirubin found in normal human gallbladder bile, and is impaired by lecithin but unaffected by cholesterol. At physiological pH in bile salt solutions, bilirubin is predominantly in its monoanion form that binds readily to the micelles. In such solutions, addition of physiological concentrations of calcium precipitates calcium bilirubinate, leaving residual bilirubin concentrations of up to 15 rc.M in 50 mM taurocholate or close to the maximum bilirubin concentrations in normal bile. Studies in which disodium bilirubinate is dissolved in bile salt solutions and pH is adjusted to the physiological range reveal that metastable supersaturation with bilirubin may occur and that a mesophase may also form in the presence of lecithin, akin to that seen with cholesterol. These results form a basis for understanding the precipitation of calcium bilirubinate from bile during pigment gallstone formation.Bilirubin is a linear tetrapyrrole of the biladiene-a,c type, consisting of two asymmetrical dipyrromethenones connected by a methylene bridge (1) (Figure 1). In the natural 1x0-Z,Z isomer that predominates in uiuo, each dipyrrolic half-molecule carries a carboxyethyl side chain that might be expected to render the pigment a highly polar, ionized and water-soluble molecule at physiological pH values. However, in its fully protonated (diacid) form, each of the two carboxyl groups forms internal hydrogen bonds with the -C=O and two >NH in the dipyrromethenone rings in the opposite half of the molecule (2). Collectively, these two trios of hydrogen bonds stabilize the bilirubin molecule in a rigid conformation that resembles a ridge tile or partially folded book (2), in

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Section: Structural Variations In Bilirubinmentioning

confidence: 99%

Bilirubin Chemistry, Ionization and Solubilization by Bile Salts

Ostrow

Celic

1984

Hepatology

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“…In contrast to pyrromethenones, the O-methyl derivatives do not isomerize photochemically (Falk, Grubmayr & Neufingerl, 1979) and have very little fluorescence (Falk & Neufingerl, 1979a). The intramolecular hydrogen bond in the O-methyl derivatives gives rise to an extremely efficient radiationless deexcitation process and is responsible for these differences (Falk & Neufingerl, 1979b).…”

Section: ~O~ch 3 ~O~chmentioning

confidence: 99%

Methoxyxanthobilirubinic acid methyl ester (methyl 3-{5-[(3-ethyl-5-methoxy-4-methyl-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-3-pyrrolyl}propanoate), C19H26N2O3

Dattagupta¹,

Meyer²,

Cullen³

et al. 1983

Acta Crystallogr C

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“…These changes are more pronounced in the 2,3-dihydrobilindiones I, 11, than in the fully unsaturated VI. Proton transfer has been suggested as a deexcitation pathway in bile pigments (Falk and Neufingerl, 1979), as well as a primary photochemical step in the phytochrome interconversion (Song et al, 1981 ) and photochemical hole burning (Friedrich et a/., 1981). According to the results represented in Table 1, intramolecular proton transfer is expected to proceed between rings D and C in I (or A and B in II), rather than 'inner' rings (B to C or cicr versa).…”

Section: Electron Derisitiesmentioning

confidence: 99%

Theoretical Studies of Biliprotein Chromophores and Related Bile Pigments by Molecular Orbital and Ramachandran Type Calculations

Scheer¹,

Formanek²,

Schneider

1982

Photochem & Photobiology

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Abstract-Ramachandran calculations have been used to gain insight into steric hindrance in bile pigments related to biliprotein chromophores. The high optical activity of denatured phycocyanin, as compared to phycoerythrin, has been related to the asymmetric substitution at ring A, which shifts the equilibrium towards the P-helical form of the chromophore. Geometric effects on the electronic structures and transitions have then been studied by molecular orbital calculations for several conjugation systems including the chromophores of phycocyanin. phytochrome P,, cations, cation radicals and tautomeric forms. For these different chromophores some general trends can be deduced. For instance, for a given change in the gross shape (e.g. either unfolding of the molecule from a cyclic-helical to a fully extended geometry, or upon out-of-plane twists of the pyrrole ring A) of the molecules under study, the predicted absorption spectra all change in a simikar way. Nonetheless, there are characteristic distinctions between the different n-systems, both in the transition energies and the charge distribution, which can be related to their known differences in spectroscopic properties and their reactivity.

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The structure of ?photobilirubin?

Cited by 23 publications

References 21 publications

Bilirubin Chemistry, Ionization and Solubilization by Bile Salts

Bilirubin Chemistry, Ionization and Solubilization by Bile Salts

Methoxyxanthobilirubinic acid methyl ester (methyl 3-{5-[(3-ethyl-5-methoxy-4-methyl-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-3-pyrrolyl}propanoate), C19H26N2O3

Theoretical Studies of Biliprotein Chromophores and Related Bile Pigments by Molecular Orbital and Ramachandran Type Calculations

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