Chlorophylls c—Occurrence, synthesis, properties, photosynthetic and evolutionary significance

Abstract The term chlorophylls c (Chls c) cover a family of chlorophylls whose common structural feature is a fully unsaturated tetrapyrrole backbone. They are widely distributed within numerous photosynthesizing groups of organisms, mainly eukaryotic algae belonging to the Chromista kingdom. The most common Chls c are Chl c1, Chl c2 and Chl c3 but several other Chl c species, named Chl c-type compounds have been also described. Chls c are important constituents of light-harvesting complexes localized in the thylakoid membranes and associated with photosystems, where they serve, together with specific carotenoids, as energetic antennae. Chls c, which have an intense Soret band and blue-shifted Q bands in comparison to chlorophyll a (Chl a), are especially efficient in harvesting blue and green light which penetrates through deep waters better than light of other wavelengths. Thus, Chls c provide energy for photosynthesis to the organisms occupying underwater habitats. Synthesis of Chls c follows many steps of the standard pathway that leads to Chl a formation. The branching point towards Chl a or Chls c is at protochlorophyllide (Pchlide), which can be converted either to Chlide a, which is the intermediate for the synthesis of chlorine-type Chls, or to Chl c2, which is an intermediate in the synthesis of other members of the Chl c family. Data on the occurrence of Chl c species as well as of other Chls is a useful tool in the taxonomy of algae, allowing us to assess the relationship among the chlorophylls and their phylogeny.