This enzyme, from a cyanophage infecting oceanic cyanobacteria of the Prochlorococcus genus, uses a four-electron reduction to carry out the reactions catalysed by EC 1.3.7.2 (15,16-dihydrobiliverdin:ferredoxin oxidoreductase) and EC 1.3.7.3 (phycoerythrobilin:ferredoxin oxidoreductase). 15,16-Dihydrobiliverdin is formed as a bound intermediate. Free 15,16-dihydrobiliverdin can also act as a substrate to form phycoerythrobilin.