Subunit size, absorption spectra and dark reversion kinetics of rye phytochrome purified in the far-red-absorbing form

Abstract

Phytochrome was protected from proteolytic attack in vitro by photo-conversion of the far-red-light-absorbing form of phytochrome (Pfr) prior to extraction and purification. Thus preparations of 124 kDalton monomer size were obtained. Their absorption spectra with maxima at 662 nm (red-light-absorbing form of phytochrome, Pr) or 732 nm (Pfr) closely resemble the absorption bands observed in vivo. Dark reversion of 124-kDalton phytochrome approaches first order kinetics with a half-life of 16 h at 25°C. A higher rate of dark reversion, as it was previously reported, can be ascribed to the 114- and 118-kDalton degradation products predominant in the preparations formerly used.