Investigation of Chromopeptides From C‐phycocyanin by Uv‐vis Absorption, Emission and Circular Dichroism Spectroscopy

Abstract

Four different chromopeptides were isolated after digestion of C‐phycocyanin with pepsin. Their UV‐vis absorption and circular dichroism spectra were measured at two different pH values without and with urea present in the buffered solutions. For one chromopeptide, fluorescence spectra and the kinetics of fluorescence decay were studied in more detail. The results are discussed in comparison with quantum‐mechanical model calculations. It is concluded that due to the interaction between the oligopeptide chain and the chromophore, the latter is present as a mixture of helical and semi‐extended forms, respectively.

Chromophore Attachment to Biliproteins: Specificity of PecE/PecF, a Lyase-Isomerase for the Photoactive 31-Cys-α84-phycoviolobilin Chromophore of Phycoerythrocyanin

“…The absorption data therefore clearly indicate that 3 1 -Cys-PCB rather than 3 1 -Cys-DBV is formed by the spontaneous addition of PCB to PecA. This conclusion is supported by peptic degradation of the addition products, whereby the chromophore is also largely (65) uncoupled from the protein. The chromopeptides absorb again close to those obtained from PC and at much shorter wavelengths than DBV-derived chromopeptides (Table 1).…”

Peptide-mediated conformational changes in bilipeptides: evidence for the occurrence of stretched species

“…Even if a hypsochromic shift of ca. [15][16][17][18] nm occurs when X is leucyl as in compounds (4)-(6), differences are smallest (2-5 nm) for compounds (7) and (8) exhibiting the smallestf-values. * On the other hand, solvent dependence of band positions does not exceed that observed for other bilatrienes.…”

“…Therefore the arguments in favour of a stretched conformation of the bilipeptides from Cphycocyanine in Tris buffer given in ref. 16 should be reconsidered. The conclusions rest upon the discrepancy between the quotient s of a helical biliverdin severely flattened by its N(21)-N( 24) bridge [(s -0.33), this value is in misleading agreement with that computed by the semi-empirical method used (s -0.36)], and those found for the chromopeptides studied (s -1.1 to -2.8).…”

BILIPROTEINS FROM THE BUTTERFLY Pieris brassicae STUDIED BY TIME‐RESOLVED FLUORESCENCE AND COHERENT ANTI‐STOKES RAMAN SPECTROSCOPY

“…It can be stated as a general rule that phycocyanins originating from blue-green algae exhibit strong bands around 1650, 1273 and 1234 cm-', respectively, if the chromophore is held in an extended conformation by interaction with the native protein (Schneider et a/., , 1988aSzalontai et al, 1985). Upon denaturation of the apoprotein, which causes the phycocyanobilin chromophore to adopt a more cyclic helical geometry, the above mentioned bands disappear and a new, strong band appears in the 162CL1630 cm-' region (Szalontai et al, 1987;Margulies and Toporowicz, 1984).…”