Abstract
1. Phytochrome was purified from etiolated oat (Avena sativa) seedlings either by gel-filtration chromatography and ion-exchange chromatography or by gel-filtration chromatography and calcium phosphate chromatography. Differences were observed in the spectral properties of phytochrome isolated by the two methods. 2. Electrophoresis of pure phytochrome at pH values between 9.0 and 6.0 showed the tendency of phytochrome to form different molecular species. Studies in the ultracentrifuge did not show a corresponding change in the sedimentation coefficient with the change in pH. 3. Tryptic digestion of electrophoretically pure phytochrome gave 17 peptides and a photoactive core. The amino acid composition of the core is reported and compared with the analysis of whole phytochrome. 4. Some properties of phytochrome isolated from Pisum sativum are compared with those of phytochrome from A. sativa. 5. The properties of phytochrome purified by other workers are compared with our findings.