Characterizing Phytochrome Photochemistry Using UV-Visible Spectroscopy in Host Cell Extracts and Purified Protein

Phytochromes are red and far-red photoreceptors widespread among life, which bind a bilin chromophore molecule. They photoswitch between two main or parent photostates: the Pr state, which absorbs red light, and the Pfr state, which absorbs far-red light. Apart from the photoconversion, there is another process called dark conversion. The phytochrome photocycle can be easily followed by ultraviolet (UV)-visible or visible spectroscopy. Through the acquisition and the later data analysis of serial UV-visible absorption spectra in either unpurified or purified protein samples, many important aspects of the phytochrome photocycle can be learned.