Purification and pigment analysis of diadinoxanthin-binding PSI-LHCI supercomplexes from Euglena gracilis strain Z.

Euglena gracilis exhibits a unique pigment profile distinct from land plants and green algae. In this study, we purified photosystem I supercomplexes containing light-harvesting complexes (PSI-LHCI) from E. gracilis strain Z and analyzed their biochemical and spectroscopic properties. The PSI-LHCI contained diadinoxanthin while lacking lutein and violaxanthin, which are characteristic of green-lineage organisms. The absorption and 77-K fluorescence spectra of Euglena PSI-LHCI showed the Qy peak of chlorophyll a at 675 nm and emission at 732 nm, respectively, comparable to land plant PSI-LHCI. These findings suggest conservation of long-wavelength chlorophylls despite distinct pigment-binding characteristics, shedding light on light-harvesting adaptations in secondary green algae.