Phycochrome d, a New Photochromic Pigment from the Blue-Green Alga, Tolypothrix distorta

A new reversibly photochromic pigment, phycochrome d, has been found in extracts of the blue-green alga Tolypothrix distorta. This phycochrome exhibits an absorbance increase in the red region (maximum at about 650 nm) when irradiated with 650 nm light, and a corresponding absorbance decrease when irradiated with 610 nm light. The absorbance difference spectrum and action spectra for in vitro conversions were determined.