Phycoerythrin (PE) is a significant protein-pigment complex. This water-soluble compound is known for its distinct reddish-pink color. Found in various photosynthetic organisms, PE has diverse applications.
What is PE Protein
PE is a light-harvesting protein pigment, classified within the phycobiliprotein family. Its primary sources are red algae (Rhodophyta) and cyanobacteria (blue-green algae). This protein’s reddish-pink to purple hue comes from chromophores, specifically phycoerythrobilin, covalently linked to its protein structure.
PE also has a fluorescent property. It absorbs light in the blue and green regions of the spectrum, with maximum absorption around 495 and 545/566 nanometers, and emits an orange-yellow fluorescence, typically around 575 to 580 nanometers. Different types of phycoerythrin, such as R-phycoerythrin (R-PE) and B-phycoerythrin (B-PE), vary slightly in their chromophore content and absorption characteristics.
Its Biological Role
Phycoerythrin performs a specialized function in photosynthesis, particularly for organisms living in environments where light penetration is limited. It acts as an accessory pigment, effectively capturing light energy that chlorophyll, the primary photosynthetic pigment, cannot efficiently absorb. This includes green and yellow light, which penetrate deeper into water columns than other wavelengths.
Once absorbed, the energy captured by phycoerythrin is efficiently transferred through other phycobiliproteins, like phycocyanin and allophycocyanin, to the reaction center chlorophyll pairs. This energy transfer allows organisms such as red algae and cyanobacteria to maximize their light utilization for photosynthesis, even in low-light conditions or deeper aquatic habitats. The ability to adapt to varying light conditions by adjusting pigment composition is known as complementary chromatic adaptation.
Uses in Science and Industry
Phycoerythrin’s fluorescent properties make it a valuable tool in scientific and industrial applications. It is used as a fluorescent marker in biomedical research due to its high sensitivity and stability. In techniques like flow cytometry, PE-conjugated antibodies label specific cell populations for identification, sorting, and analysis based on fluorescent signals.
The protein also finds application in immunofluorescence, where it labels antibodies to visualize specific proteins or molecules within cells and tissues. Its bright fluorescence and resistance to photobleaching make it suitable for advanced microscopy techniques and microarray analysis. Beyond scientific research, phycoerythrin’s vibrant pink-red color and antioxidant properties mean it is explored as a natural food coloring agent in products like chewing gums, jellies, and dairy items. It is also used in cosmetics, such as lipsticks and eyeliners, and in emerging fields like photodynamic therapies.