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

Bilipeptides, C-Phycocyanin, High Resolution N M R Spectra, Photoisom erization, Phytochrom e Chromopeptides were prepared by pepsin digestion of C-phycocyanin isolated from the cyano bacterium Spirulina m axim a and o f phytochrom e isolated from seedlings o f Avena sativa L. The chromopeptides were characterized by am ino acid analysis. The Z Z Z configurated chrom ophore of the phycocyanin peptide was transformed into its Z Z E configurated isom er by the m ethod of Falk et al. (Mh. C hem ie 111, [159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175] 1980) which had previously been applied to biliverdins. The 500 MHz 'H N M R spectrum o f the Z Z E configurated chrom opeptides confirmed that its chromophore has the 15 E configuration. Irradiation yielded the Z Z Z configurated isom er for which the 'H N M R spectrum was also recorded. N ative phytochrom e 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. studies. Similar studies with phycocyanin, the light harvesting chrom oprotein of blue-green algae and red algae [6 ] showed, that its chrom ophore (Structure lb ) differs from phytochrom obilin only in the side chain at C -l8 , which is an ethyl group in phycocyanobilin and a vinyl group in phytochrom o bilin [7,8 ], R 1a : r = CH = CH2 1b : R= C2 h 5

Phytochrome photoconversion

“…Time-resolved fluorescence kinetics of native oat phyA showed no deuterium isotope effect, ruling out proton transfer as a primary photochemical step (Brock et al 1987). This confirms the postulate (Thummler et al 1983) that the primary photochemical step is a Z->E isomerization of the chromophore 15,16 double bond.…”

Molecular cloning of a novel phytochrome gene of the moss Ceratodon purpureus which encodes a putative light-regulated protein kinase

“…The predicted structure of PhyCer implicates that the NH 2 terminus of phytochrome undergoes light-dependent conformational changes, triggered by a reversible Z-E isomerization of the chromophore [31,46], which are transmitted to the COOH-terminus which in turn is linked with a cellular phosphorylating cascade.…”

Infrared spectroscopy of phytochrome and model pigments

“…Lack of a deuterium isotope effect for phototransformation of PI into the first intermediate as detected by low-temperature ultravioletjvisible absorption spectroscopy also argued against tautomerization of the chromophore or proton transfer from chromophore to the protein as the primary photoreaction (Eilfeld and Rudiger, 1986). Analysis of small chromopeptides obtained by proteolysis of the PI and PfI forms revealed different configurations for the chromophore at the 15,16-double bond (Rudiger et al, 1983;Thiimmler et al, 1983). Therefore, Z+ E isomerization at C15/16 was considered as a good candidate for the primary photoreaction (Rudiger et al, 1985) ( Fig.…”