Chromophore structure of the physiologically active form (P(fr)) of phytochrome.

Chromopeptides were prepared by proteolytic digestion of phytochrome (far-red absorbing form, P(fr)) and of phycocyanin. The phycocyanobilin peptide, the chromophore of which is Z,Z,Z-configurated, was modified to the Z,Z,E isomeric chromophore. It has been demonstrated earlier that the P(fr) chromopeptide and the Z,Z,E-configurated phycocyanin chromopeptide behave similarly with regard to spectral and chromatographic properties and reactivity. We present evidence here, obtained by high-resolution (1)H NMR spectroscopy, that both the modified phycocyanobilin chromophore and the phytochrome chromophore obtained directly from P(fr) are 15E-configurated.