It lacks the phytol side-chain of chlorophyll and the reduced pyrrole in ring D.[2] Protochlorophyllide is highly fluorescent; mutants that accumulate it glow red if irradiated with blue light.

[6] This enzyme might be evolutionary older but (being similar to nitrogenase) is highly sensitive to free oxygen and does not work if its concentration exceeds about 3%.

Angiosperms have lost the dark-operative form and rely on 3 slightly different copies of light-dependent version, frequently abbreviated as POR A, B, and C. Gymnosperms have much more copies of the similar gene (Loblolly pine has about 11 Loblolly Pine (Pinus taeda L.) Contains Multiple Expressed Genes Encoding Light-Dependent NADPH:Protochlorophyllide Oxidoreductase (POR)).

Plants that are fed by ALA accumulate high and toxic levels of protochlorophyllide, as do mutants with a disrupted regulatory system.

Green regions survive the subsequent nights, likely because the synthesis of chlorophyll in the mature leaf tissue is greatly reduced anyway.

In a different manner, the Chlamydomonas regulatory protein is more complex: It is larger, crosses the thylakoid membrane twice rather than once, contains more protein-protein interactions sites, and even undergoes alternative splicing.