Pigments which are not directly involved in photosynthesis but have the ability to absorb light and transfer it to the principal photosynthetic pigments are called as Accessory pigments. Phycobilins are water soluble pigments that are fairly joined to a protein, which acts as a accessory pigment in photosynthesis. Phycocyanobilin and Phycoerythrobilin are major phycobilins.
2. Contents
• Introduction
• Phycobilins
• Phycocyanin
• Phycoerythrin
• Comparison between phycocyanin and phycoerythrin
• Phycobilins in photosynthesis
• Conclusion
• Reference
3. Introduction
• Pigments are organic compounds which absorbs certain
wavelength of visible light and reflects the other.
• Each pigment has its own characteristic color.
• The photosynthetic pigments in algae are classified into 3
categories:
1. Chlorophylls
2. Carotenoids and xanthophylls
3. Phycobilins
• The pigments which are not directly involved in
photosynthesis but have the ability to absorb light and transfer
it to the principal photosynthetic pigments are called as
Accessory pigments.
• F. E Fritsch classified algae based on their pigmentation.
4. Phycobilins
• Phycobilins are water soluble pigments that are fairly joined to
a protein, the combination being referred to as biliproteins.
• Phycoblinins are tetrapyrroles, the four pyrroles in
phycobilins occur in an open chain.
• 300-800 phycobilins assemble and organize into
phycobilisomes which are about 40 nm in diameter and are
associated with the outer surfaces of lamellar membranes in
Cyanobacteria and Rhodophytes.
• They usually have their major absorption bands from 520-
670nm.
• These pigments are higher in concentration in many
Cyanophycean and Rhodophycean members and are
responsible for the characteristic color of the organism.
• The major phycobilins are
1. Phycocyanobilin
2. Phycoerythrobilin
5. Phycocyanin
• Phycocyanobilin and the protein to which it is covalently
attached together constitute Phycocyanin.
• It appears bluish color because it absorbs strongly from 610-
660 nm.
• It absorbs green, yellow and red light and transmit blue.
• It is the main phycobilin in the Cyanophycean members and is
also found in members of Rhodophyta.
• Phycocyanin are sub divided into 3 types:
a) R-Phycocyanin (Rhodophyta)
b) C-phycocyanin (Cyanophyta)
c) Allophycocyanin
6. Figure 1: Arthrospira jenneri Figure 2: Oscillatoria sancta
Cyanophycean members exhibiting blue-green color due to the
presence of Phycocyanin pigment.
7. • Molecular formula: C33H38N4O6
• It has 9 conjugated double bonds and its λmax occurs in the red
region.
Figure 3 : Phycocyanobilin
8. Phycoerythrin
• Phycoerthrobilin along with the protein to which it is
covalently attached is called Phycoerythrin.
• Phycoerythrin is reddish because it absorbs green and has at
least one main band between 530-570 nm.
• It occurs throughout the red algae and in some Cyanobacteria.
• Phycoerythrin are of three types
a) R- Phycoerythrin
b) B- Phycoerythrin
c) C- Phycoerythrin (Cyanophyta)
• Due to photodestruction of phycoerythrin, many red alga do
not appear reddish at all, and a full range of pigment is
exhibited like violet, purple, black, yellow and greenish
forms.
(Rhodophyta)
9. Figure 4 : Polysiphonia elongata Figure 5: Gelidium corneum
Rhodophycean members exhibiting red color due to the
presence of Phycoerythrin pigment.
10. • Molecular formula: C33H38N4O6
• It has 7 double bonds in the main conjugated system and
absorbs maximally in the green region of the spectrum.
• Spectroscopic and biochemical studies have shown that energy
from light absorbed by phycoerythrobilin must first be
transferred to phycocyanobilin before it can reach chlorophyll
and contribute to photosynthesis.
Figure 5: Structure of Phycoerythrin.
11. Comparison between Phycocyanin and Phycoerythrin
Phycocyanobilin
• Absorbs green, yellow and
red light and transmit blue
• Absorbs strongly from 610-
660 nm.
• Main phycobilin in the
Cyanophycean members
and is found in members of
Rhodophyta.
• 9 conjugated double bonds
and its λmax occurs in the red
region.
• Independently can harvest
the light.
Phycoerythrobilin
• Absorbs green and transmit
red.
• Absorbs strongly from 530-
570 nm.
• It occurs throughout the red
algae and in some
Cyanophycean members.
• 7 double bonds in the main
conjugated system and its
λmax occurs in the green
region of the spectrum.
• Presence of phycocyanobilin
is necessary for light-
harvesting function
12. Phycobilins in photosynthesis
• The energy of photons of light absorbed by the phycobilin is
transferred to chlorophyll-a molecules in the reaction centers
by the Förster excitation transfer mechanism.
• The indirectly photoexcited chlorophylls in the reaction
centers then undergo the photosynthetic ‘light reaction’ —
essentially a photoionization.
• The phycobilisomes act as a light-absorbing antenna
for photosynthesis, and are able to efficiently absorb light in
the green and orange spectral region where chlorophyll
absorbs poorly.
• The pathway of energy transfer is
Phycoerythrin
(λmax =565)
Phycocyanin
(λmax =620-638)
Chlorophyll a
13. Conclusion
• Phycobilins are the water soluble pigments which give
characteristic color to the organism. They play an important
role in photosynthesis as they increase the range of absorption
of wavelength. It enables the continuity of life in the benthic
region of oceans where most of the Rhodophytes exists.
14. References
1. Bold, H. C. and Wynne, M.J. 1978. Introduction to the algae-
Structure & reproduction. Prentice Hall. Pp.451-454
2. Lee, R. E. 2008. Phycology. 4th Edn. Cambridge Univ. press,
New york. Pp.17-19
3. Singh, V., Pande, P.C. and Jain, D.K. 2014. A Textbook of
Botany. 4th Edn. Rastogi Pub.Co. New Delhi. Pp.6, 27-29.
4. https://www.ncbi.nlm.nih.gov/compound/6443764
5. https://pubchem.ncbi.nlm.nih.gov/compound/6438349
6. www.algaebase.org
