Chromopeptides from Phytochrome and Phycocyanin. NMR Studies of the Pfr and Pr 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 m axim a and of phytochrome isolated from seedlings of Avena sativa L. The chromopeptides were characterized by amino acidanalysis. The ZZZ configurated chrom ophore of the phycocyanin peptide was transformed into its ZZE configurated isomer by the m ethod of Falk et al. (Mh. Chem ie 111, 159-175, 1980) which had previously been applied to biliverdins. The 500 MHz 1H NMR spectrum of the ZZE configurated chrom opeptides confirmed that its chromophore has the 15 E configuration. Irradiation yielded the ZZZ configurated isomer for which the 1H NMR spectrum was also recorded. Native phytochrome was irradiated at 660 nm to yield the maximum am ount of the Pfr from (about 75% of total phytochrome). By digestion in the dark the previously described Pfr chrom opeptide was obtained. The 500 MHz 1H NMR spectrum was compared with that of the ZZE phycocyanin peptide. It confirmed the 15 E configuration of the Pfr chrom opeptide. Irradiation yielded the 15 Z configurated Pr chrom opeptide. Comparison of the high resolution 1H NMR spectra of Pfr and Pr chrom opeptides revealed that not only the chrom ophore resonances but also those of some amino acids are changed by the Pfr → Pr chrom opeptide phototransformation. The results are discussed in terms of chrom ophore amino acid interaction. © 1983, Walter de Gruyter. All rights reserved.