Ligandin reverses bilirubin inhibition of liver mitochondrial respiration in vitro

Ligandin, an abundant cytoplasmic binding protein of bilirubin and other ligands in liver cells, completely prevented the inhibitory effect of bilirubin on respiration and oxidative phosphorylation by isolated rat liver mitochondria. At equimolar concentrations of bilirubin and ligandin or human serum albumin, mitochondrial respiration was fully restored to control values. At greater ratios of bilirubin and ligandin or human serum albumin, the latter had a stronger protective effect. These studies suggest that ligandin may have a physiologic role in protecting mitochondrial systems against bilirubin toxicity.