On the Reactivity of Native Phytochrome

Previous phytochrome models were based on experimental results obtained only with proteolytically degraded phytochrome. The reactivity of native phytochrome, in both the Pr and the Pfr form, towards 8-anilinonaphthalene-1-sulfonate (ANS), urea, and ethylene glycol is described here. Whereas native phytochrome in the Pfr form is only very slowly bleached by ANS, immediate bleaching occurs with ANS treated Pr during red irradiation. The bleached form, Pr , can be converted into Pr by prolonged far-red irradiation. A tentative model for native phytochrome is proposed which explains the effects of phototransformation, ANS binding and partial proteolysis.