Lumirubin

Figure 22-2. Photobilirubins. Light-induced isomerization of bilirubin at the 4- and 15-double bonds produces photoisomers that are water soluble. In addition, bilirubin can be photochemically cyclized to water-soluble lumirubin.

For many years, phototherapy has been the standard treatment of neonatal hyperbilirubinemia. The effectiveness of this form of therapy is based on the ability of photons of the appropriate wavelength to convert the intramolecularly H-bonded bilirubin IXa with its low solubility into photoisomers of bilirubin in which the normal Z,Z stereochemistry at the 4- and 15-positions is changed, resulting in photoisomers that are more water soluble. In addition, bilirubin can be converted into the cyclic lumirubin, which is soluble and can be excreted in the urine (Fig. 22-2). Photoproducts can also be excreted through the liver pathway without... 

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