Why biliverdin is reduced to bilirubin? It isn't toxic, it is water soluble.. Then why convert it to bilirubin?
According to some, biliverdin works just fine. Mammals have evolved the energetically expensive, potentially harmful and apparently unnecessary capacity to reduce biliverdin.
According to others, the conversion is not a wasteful process. Bilirubin is a cytoprotectant and that's why biliverdin is converted into bilirubin. It's also a physiological anti oxidant!