A common example is haemoglobin, which contains a heme cofactor, which is the iron-containing molecule that makes oxygenated blood appear red.
A single chromoprotein can act as both a phytochrome and a phototropin due to the presence and processing of multiple chromophores.
The chromophore is derived from Glu-63, Tyr-64 and Gly-65 and the phenolic group of Tyr-64 plays a vital role in the formation of a conjugated system with the imidazolidone moiety resulting a high absorbance in the absorption spectrum of chromoprotein in the excited state.
mRFP1, the monomeric red fluorescent protein,[6] which also displays distinguishable color under ambient light, was found to be less toxic.
Chromoproteins are valuable in synthetic biology, genetic engineering, and biotechnology as visible markers for tracking gene expression, assaying cellular functions and creating colorful biosensors.