proteinpigment

Protein pigment is a term used to describe pigments that are associated with proteins, either because the pigment molecule is the prosthetic group of a protein or because a protein scaffold binds a pigment tightly and contributes to its optical properties. In these systems, the color arises from the pigment’s electronic structure, which is modulated by its protein environment.

Examples include heme-containing proteins (hemoglobins, myoglobins, and cytochromes) whose colors stem from the heme iron complex, and pigment–protein complexes known as phycobiliproteins (phycoerythrin, phycocyanin, allophycocyanin) used in light harvesting by cyanobacteria and red algae. Fluorescent proteins, such as the green fluorescent protein (GFP) and its variants, are chromoproteins in which a chromophore forms in situ within the protein, giving rise to bright fluorescence.

Functionally, protein pigments participate in color production, light absorption, and energy transfer. In photosynthetic organisms, pigment–protein complexes collect light and funnel energy to reaction centers. In animals and microbes, heme proteins participate in oxygen transport, electron transfer, and catalysis; in laboratory settings, fluorescent proteins enable imaging and tracking of cellular processes.

Research and applications include spectroscopy of pigment–protein complexes, development of fluorescent protein tags for microscopy, and natural pigment sources for dyes. The stability, brightness, and spectral properties of protein pigments can be tuned by mutations to the protein scaffold.