chromophore phytochrome chromophore A chromophore that is a linear tetrapyrrolic prosthetic group covalently attached to a large soluble protein phytochrome. Light absorption by the phytochrome chromophore triggers photoconversion between two spectrally distinct forms of the photoreceptor: Pr, the red light absorbing form, and Pfr, the far-red light absorbing form. chebi_ontology CHEBI:82632 phytochrome chromophores PMID:2909515