Pigment structure in the light-harvesting protein of the siphonous green alga Codium fragile

The siphonaxanthin-siphonein-chlorophyll-a/b-binding protein (SCP), a trimeric light-harvesting complex isolated from photosystem II of the siphonous green alga Codium fragile, binds carotenoid siphonaxanthin (Sx) and/or its ester siphonein in place lutein, addition to chlorophylls a/b and neoxanthin. SCP exhibits higher content chlorophyll b (Chl-b) than counterpart plants, (LHCII), increasing relative absorption blue-green light for photosynthesis. Using low temperature resonance Raman spectroscopies, we reveal presence two non-equivalent Sx molecules SCP, assign their peaks at 501 535 nm. red-absorbing population significant distortion that is reminiscent lutein 2 LHCII. Unexpected enhancement modes Chls-b allows an unequivocal description seven nine Chls-b, six distinct Chl-a populations this protein.