Chromopeptides from Phytochrome and Phycocyanin. NM R Studies o f the P_fr and P_r Chromophore of Phytochrome and E,Z Isomeric Chromophores of Phycocyanin

Abstract

Chromopeptides were prepared by pepsin digestion of C-phycocyanin isolated from the cyano­bacterium Spirulina maxima and of phytochrome isolated from seedlings of Avena sativa L. The chromopeptides were characterized by amino acid analysis. The ZZZ configurated chromophore of the phycocyanin peptide was transformed into its ZZE 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 1 HNMR spectrum of the ZZE configurated chromopeptides confirmed that its chromophore has the 15 E configuration. Irradiation yielded the ZZZ configurated isomer for which the 1 H NMR spectrum was also recorded. Native phytochrome was irradiated at 660 nm to yield the maximum amount of the P fr from (about 75% of total phytochrome). By digestion in the dark the previously described P fr chromopeptide was obtained. The 500 MHz 1 H NMR spectrum was compared with that of the ZZE phycocyanin peptide. It confirmed the 15 E con­figuration of the P fr chromopeptide. Irradiation yielded the 15 Z configurated P r chromopeptide. Comparison of the high resolution 1 HNMR spectra of P fr and P r chromopeptides revealed that not only the chromophore resonances but also those of some amino acids are changed by the P fr → P r chromopeptide phototransformation. The results are discussed in terms of chromophore amino acid interaction.