<P> Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases . It is responsible for the yellow color of bruises and the yellow discoloration in jaundice . Its subsequent breakdown products, such as stercobilin, cause the brown color of faeces . A different breakdown product, urobilin, is the main component of the straw - yellow color in urine . </P> <P> It has also been found in plants . </P> <P> Bilirubin consists of an open chain of four pyrrole - like rings (tetrapyrrole). In heme, these four rings are connected into a larger ring, called a porphyrin ring . </P> <P> Bilirubin can be "conjugated" with a molecule of glucuronic acid which makes it soluble in water (see below). This is an example of glucuronidation . </P>

The enzyme that conjugates bilirubin in the hepatocyte is