A viewpoint: Why chlorophyll a?

Research output: Contribution to journalReview article


Chlorophyll a (Chl a) serves a dual role in
oxygenic photosynthesis: in light harvesting as well as in
converting energy of absorbed photons to chemical energy.
No other Chl is as omnipresent in oxygenic photosynthesis
as is Chl a, and this is particularly true if we include Chl a2,
(=[8-vinyl]-Chl a), which occurs in Prochlorococcus, as a
type of Chl a. One exception to this near universal pattern
is Chl d, which is found in some cyanobacteria that live in
filtered light that is enriched in wavelengths [700 nm.
They trap the long wavelength electronic excitation, and
convert it into chemical energy. In this Viewpoint, we have
traced the possible reasons for the near ubiquity of Chl a
for its use in the primary photochemistry of Photosystem II
(PS II) that leads to water oxidation and of Photosystem I
(PS I) that leads to ferredoxin reduction. Chl a appears to
be unique and irreplaceable, particularly if global scale
oxygenic photosynthesis is considered. Its uniqueness is
determined by its physicochemical properties, but there is
more. Other contributing factors include specially tailored
protein environments, and functional compatibility with
neighboring electron transporting cofactors. Thus, the same
molecule, Chl a in vivo, is capable of generating a radical
cation at ?1 V or higher (in PS II), a radical anion at -1 V
or lower (in PS I), or of being completely redox silent (in
antenna holochromes).


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences


  • Photosystem II, Evolution of photosystems _ Oxygenic photosynthesis, Color of plants, Cyanobacteria, Chlorophylls in proteins, Chlorophyll a, Chlorophyll d, Reaction centers, Chemistry of chlorophylls, Photosystem I, Spectra of chlorophylls
Original languageEnglish
Pages (from-to)85-98
JournalPhotosynthesis Research
Issue number2
Publication statusPublished - 2009
Publication categoryResearch