Binding properties of the degraded 59kD phytochrome from etiolated Avena sativa seedlings to liposomes and Cibacron Blue dye were examined. In contrast with the native 124kD and partially degraded 118kD phytochromes, the farred light absorbing(Pfr) forms of the 59kD phytochrome hinds to liposomes and Cibacron Blue dye via electrostatic interactions. Results indicate that the 59kD Pfr does not hold a hydrophobic surface which is exposed upon Pr to Pfr phototransformation of the 124 and 118kD phytochromes. Since a relatively extensive hydrophobic region is located in the chromophore bearing domain(59kD) of phytochrome(Hershey et al., Nuc. Acids Res., 13, 8543, 1986), the 55kD tryptic domain from the C-terminus plays an important role on the exposure of the hydrophobic area in the 118 and 124 Pfr to occur.