Chromatographic behaviour of phytochrome following its in vivo phototransformation

Soluble phytochrome of maize coleoptiles does not readily permeateSephadex G200 and is eluted in the void volume as a single species.The exclusion by Sephadex G200 is not due to molecular aggregation.This property of maize phytochrome is found with material extractedfrom both the dark grown or far red and red irradiated tissues;and at 4?C elution proceeds under normal laboratory lightingas it does in darkness or under a green safelight. During chromatographyon Sepharose 4B of soluble extracts of maize coleoptiles containingsoluble phytochrome it behaves as a single species and it iseluted at a position similar to that of catalase. Phytochromerecovered from the phytochrome-binding site complex which isformed inside cells of coleoptiles following irradiation withred light is eluted ahead of catalase suggesting that it hasgained in size. A further size increase (about 2-fold) is observedwhen the particulate fraction containing the complex is treatedwith Triton X100. Control experiments demonstrate that the sizeincrease is due neither to molecular aggregation nor to grossprotein-denaturation but is probably due to a change in molecularconfiguration. (Received May 25, 1976; )