Preparation and Properties of Chromopeptides from the Pfr Form of Phytochrome

Abstract Chromopeptides were prepared from the Pfr form of phytochrome by pepsin digestion. After separation from colorless peptides and Pr peptides by column chromatography, spectral characteristics of this Pfr peptide were determined (λ1max = 610nm, λ2max = 380nm in acid methanol). Irradiation of Pfr peptide produces Pr peptide without liberation of a detectable compound. The Pfr peptide is more sensitive to oxidation and reduction than the Pr peptide. Oxidation with iodine and reduction with dithionite leads to partial chemoconversion of the Pfr peptide to the Pr peptide. The results favor the model of cis-trans isomerization for the Pr ⇌ Pfr transformation.