Chromopeptides from phytochrome. The structure and linkage of the PR form of the phytochrome chromophore

The isolation and chromatographic purification of chromophore-containing peptides from the P{sub R} form of phytochrome treated with pepsin and thermolysin are described. From the amino acid sequence and {sup 1}H NMR spectral analysis of phytochromobiliundeca peptide (2) , the structure of the P{sub R) phytochrome chromophore and the nature of the thioether linkage joining pigment to peptide have been established. Confirmatory evidence was obtained from similar analysis of phytochromobilioctapeptide (3) . The implications of this structural assignment with respect to the mechanism of the P{sub R} to P{sub FR} phototransformation is considered.