Characterisation of hydrophobic peptides by RP-HPLC from different spectral forms of LH2 isolated from Rps. palustris

The separation of light-harvesting peptides by RP-HPLC is notoriously diffi cult due to the typically strong interaction of peptides with the column ma trix, their relatively low solubility in the mobile phase and the tendency for non-specific aggregation during sample preparation. This paper illustra tes a reproducible method for investigating the composition of four spectra lly different forms of LH2 isolated from Rps. palustris. The method contras ts with previous attempts to isolate peptides from these multi-LH2 complexe s and uses the well characterised B800-850 complex from Rps. acidophila as a test of reliability. Three pairs of LH2 peptides, alpha beta(a), alpha be ta(b) and alpha beta(d), were identified from Rps. palustris grown under hi gh- (7000 lux) or intermediate- (1000 lux) light conditions. At lower light (300 and 90 lux), alpha beta(b) was absent, and the level of alpha beta(a) was significantly reduced. Results show that alpha beta(a) and alpha beta( b) peptides form the high light B800-850 complex, whereas the low light LH2 complex is only composed of alpha beta(d) peptides and resembles the B800- 820 complex from Rps. acidophila by sequence homology. The absorption spect rum of this complex has a single peak centred on 800 nm and appears to be a novel LH2 complex. At low light growth conditions, this B800 species is th e predominant LH2 complex in Rps. palustris and indicates that peptide expr ession is a crucial factor in adapting to different light intensities.