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A viewpoint: Why chlorophyll a?

  • Lars Olof Björn
  • George C. Papageorgiou
  • Robert E. Blankenship
  • [unknown] Govindjee
Publishing year: 2009
Language: English
Pages: 85-98
Publication/Series: Photosynthesis Research
Volume: 99
Issue: 2
Document type: Journal article review
Publisher: Springer

Abstract english

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).


  • 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


  • Photobiology
  • Photobiology-lup-obsolete
  • ISSN: 0166-8595
Lars Olof Björn
E-mail: lars_olof [dot] bjorn [at] biol [dot] lu [dot] se

Professor emeritus

Molecular Cell Biology

+46 46 222 72 53