What is "urobilin"

Urobilin \U`ro*bi"lin\, n. [1st uro- + bile + -in.] (Physiol. Chem.) A yellow pigment identical with hydrobilirubin, abundant in the highly colored urine of fever, and also present in normal urine. See Urochrome.

n. (context biochemistry English) A yellow linear tetrapyrrole resulting from the breakdown of heme, produced when urobilinogen is oxidized by intestinal bacteria.

n. brown bile pigment formed from urobilinogens and found in feces and in small amounts in urine

Urobilin or urochrome is the chemical primarily responsible for the yellow color of urine. It is a linear tetrapyrrole compound that, along with the related compound urobilinogen, are degradation products of the cyclic tetrapyrrole heme.