Biochemistry , Photosystem 2

1. Protein complexes of
photo system II

2. Photo system II
Photo system II (PSII) converts sunlight into
chemical energy . Photo system II (PSII) is a large
pigment–protein complex embedded in the
thylakoid membrane of all oxygenic photosynthetic
organisms: Cyanobacteria, algae, and plants. In this
water molecules split into protons, electrons, and
molecular oxygen, ultimately yielding the high-
energy molecules ATP and NADPH . The water-
splitting reaction is catalyzed by a Mn4CaO5

3. • Photo system II contains at least 99 cofactors: 35
chlorophyll a, 12 beta-carotene, two pheophytin,
two plastoquinone, two heme, one bicarbonate, 20
lipids .
• Photo system II reaction center contains five
proteins D1, D2, PsbE, PsbF, and PsbI .
• Algae and higher plants have two photo system .
Photosynthesis bacteria have one photo system .

5. Reaction center consists
chlorophyll P680
plastoquinone
water
pheophytin
heme B
beta carotene

7. Subunit Family Function
D1
Photo synthetic
reaction center protein
family
Reaction center
protein , binds chl
P680 , pheophytin
,beta carotene ,
quinone and Mn
center
D2 Reaction center
protein
CP43
(B)
Photo system II light
harvesting protein
family
Binds manganese
center
CP47
(C)
O Manganese stabilizing
protein family
Manganese stabilizing
protein

8. cofactor / coenzyme Function
Chlorophyll Absorb light energy into chemical
energy
Beta carotene Quench excess photoexidation
energy
Heme B Secondary / protective electron
carrier
Plastoquinone Mobile intra thylakoid membrane
electron carrier
Manganese center Oxygen evolving center
Pheophytin Primary electron acceptor