In enzymology, a phytochromobilin:ferredoxin oxidoreductase is an enzyme that catalyzes the chemical reaction Thus, the two substrates of this enzyme are (3Z)-phytochromobilin and oxidized ferredoxin, whereas its two products are biliverdin IXalpha and reduced ferredoxin. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with an iron-sulfur protein as acceptor. The systematic name of this enzyme class is (3Z)-phytochromobilin:ferredoxin oxidoreductase. Other names in common use include HY2, PPhiB synthase, and phytochromobilin synthase. This enzyme participates in porphyrin and chlorophyll metabolism.