Interaction of bilirubin and indocyanine green with the binding and conjugation of sulfobromophthalein by rat liver cytosol proteins.

: The interaction of bilirubin and indocyanine green with sulfobromophthalein (BSP) binding and conjugation by rat liver cytosol proteins was studied. BSP bound to cytosol proteins X, ligandin and Z and the BSP-glutathione conjugate were isolated by sephadex gel chromatography. Neither bilirubin nor indocyanine green affected the binding of BSP to ligandin and Z protein. However, indocyanine green did significantly reduce BSP conjugation in both in vitro and in vivo experiments. Diethyl maleate significantly reduced liver glutathione levels and BSP conjugation. It is suggested that indocyanine gree competitively binds at the ligandin catalytic site whereas the primary binding site for bilirubin is probably a noncatalytic site.