The Necessity for beta-Carotene in the 518 Nanometer Absorbance Change.

The identity of the pigment responsible for the light-induced 518 nanometer absorbance change was investigated by extraction and reconstitution of spinach chloroplasts. Heptane extraction of carotene and quinones from lyophilized chloroplasts removes absorbance changes at 518 and 475 nanometers activated by both laser flash and continuous illumination. Some electron transport activity is always present, even in carotene- and quinone-depleted chloroplasts, but the light-induced pH increase disappears following the first extraction step. Readdition of pure beta-carotene partially restores the 518 and 475 nanometer absorbance changes.