text: Biosynthesis of coelenterazine in Metridia starts from two molecules of tyrosine and one molecule of phenylalanine, and some researchers believe this comes in the form of a cyclized "Phe-Tyr-Tyr" (FYY) peptide.
  Many members of the genus Metridia also produce luciferases that use this compound, some of which are secreted into extracellular space, an unusual property for luciferases.