Chromopeptides from Phytochrome and Phycocyanin. NMR Studies of the Pfr and Pr Chromophore of Phytochrome and EyZ Isomeric Chromophores of Phycocyanin

Bilipeptides, C-Phycocyanin, High Resolution NMR Spectra, Photoisomerization, Phytochrome Chromopeptides were prepared by pepsin digestion of C-phycocyanin isolated from the cyano­ bacterium Spirulina m axim a and of phytochrome isolated from seedlings of Avena sativa L. The chromopeptides were characterized by amino acid analysis. The Z Z Z configurated chromophore of the phycocyanin peptide was transformed into its Z Z E configurated isomer by the method of Falk et al. (Mh. Chemie 111, 159—175, 1980) which had previously been applied to biliverdins. The 500 MHz 'H N M R spectrum of the Z Z E configurated chromopeptides confirmed that its chromophore has the 15 E configuration. Irradiation yielded the Z Z Z configurated isomer for which the 'H NMR spectrum was also recorded. Native phytochrome was irradiated at 660 nm to yield the maximum amount of the Pfr from (about 75% of total phytochrome). By digestion in the dark the previously described Pfr chromopeptide was obtained. The 500 MHz 'H NM R spectrum was compared with that of the Z Z E phycocyanin peptide. It confirmed the 15 £ con­ figuration of the Pfr chromopeptide. Irradiation yielded the 15 Z configurated Pr chromopeptide. Comparison of the high resolution 'H N M R spectra of Pfr and Pr chromopeptides revealed that not only the chromophore resonances but also those of some amino acids are changed by the Pfr -*■ Pr chromopeptide phototransformation. The results are discussed in terms of chromophore amino acid interaction.