Isolation and characterization of a major chlorophyll a c2 light-harvesting protein from a Chroomonas species (Cryptophyceae)

Three chlorophyll-protein complexes of a Chroomonas species (Cryptophyceae) have been separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The two bands at 100 and 42 kDa are Complex I (CP I) and Complex IV (CP IV), the ubiquitous chlorophyll a-proteins associated with Photosystems I and II, respectively. The third 55 kDa band, which had two peptide subunits (24 and 20 kDa), contained both chlorophyll a and chlorophyll c₂ in a molar ratio of 1.4 chlorophyll a to 1 chlorophyll c₂ ( chlorophyll a chlorophyll c₂ ratio in whole cells = 4). A chlorophyll a c₂ fraction with similar spectral and electrophoretic properties was isolated by digitonin-sucrose density gradient centrifugation. This fraction had no photochemical activity and contained only a single carotenoid species with absorbance maxima in methanol at 424, 448 and 476 nm. Efficient energy transfer from chlorophyll c₂ to chlorophyll a occurred in the complex.