Gerald F. Deitzer gd3 at
Fri Jun 2 08:01:33 EST 2000

Dear Dave,

Phycobilins are accessory pigments associated with protein complexes
called phycobilisomes in
Cyanobacteria (Cyanophyta) and red algae (Rhodophyta).  They are not
soluble in the stroma,
but rather are attached as peripheral membrane protein complexes to the
stromal side if the core
complex of the photosystem II which are integral membrane membrane
proteins.  They function in much the same way as the light harvesting
complexes in green algae (Chlorophyta) and higher
plants. The evolution of photosynthetic eukaryotes was reviewed recently
by Chuck Delwiche
(Delwiche, CF, 1999, Tracing the thread of plastid diversity through the
tapestry of life. The
American Naturalist 154: S164-S177) and the structure and evolution of
phycobilisomes has
been reviewed by Beth Gantt (Gantt, E, 1996, Pigment protein complexes
and the concept of the
photosynthetic unit: Chlorophyll complexes and phycobilisomes.
Photosynthesis Research 48:

There is; however, one phycobilin that is soluble, but it is in the
cytoplasm of all photosynthetic
auxotrophs and serves no function as an antenna pigment.  It is the
photoregulatory pigment
known as phytochrome that contains a chromophore called
phytochromobilin.  This chromophore behaves spectrally just like
phycocyanin, but is structurally more like phycoerythrin.  It differs
from these phycobiliproteins primarily in the structure and function of
the protein with which it
associates.  Clark Legarias is running a symposium on the evolution of
photoreceptors at the Plant Physiology meeting in San Diego this summer
and the abstracts for these talks can be found on the ASPP web page

Sorry, I got carried away.

Gerry Deitzer

David Haas wrote:

  What is the role of phycobilins in photosynthesis?

   I know that the lipid soluble accessory pigments in the thyakoids
  are part of the pigment systems and as such transfer photon
  energy to the reaction center. Phycobilins are, as i understand,
  water soluble and found in the stroma. So what do they do and how
  do they do it?   Anybody know?

  D. Haas


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