The Electron Transport Pathway from
Water (H2O) to NADP+ (the Nicotinamide Adenine
Dinucleotide Phosphate, oxidized form).
Many versions of the Z-scheme are available in
the literature.This particular diagram was developed by
Wilbert Veit and Govindjee, 2000,
and can be also found at molecadv.com.
Abbreviations used are (from left to the right of the
diagram): Mn for a manganese complex containing 4
Mn atoms, bound to Photosystem II (PSII) reaction center;
Tyr for a particular tyrosine in PSII; O2 for
oxygen; H+ for protons; P680 for the
reaction center chlorophyll (Chl) in
PSII: it is the primary electron donor of PSII; Excited (Chl)
P680 for P680* that has the energy of the
photon of light; Pheo for pheophytin molecule (the
primary electron acceptor of PSII; it is like a
chlorophyll a molecule where magnesium (in its
center) has been replaced by two "H"s); QA for a
plastoquinone molecule tightly bound to PSII; QB for
another plastoquinone molecule that is loosely bound to
PSII; FeS for Rieske Iron Sulfur protein; Cyt.
f for Cytochrome f; Cytb6 (L and H) for Cytochrome b6 (of Low and High Energy); PC for copper
protein plastocyanin; P700 for the reaction center
chlorophyll(Chl;actually a dimer, i.e., two molecules together) of PSI; it is the
primary electron donor of PSI; Excited (Chl) P700 for P700*
that has the energy of the photon of light; Ao for
a special chlorophyll a molecule (primary electron
acceptor of PSI); A1 for a
phylloquinone (Vitamin K) molecule; FX, FA,
and FB are three separate Iron Sulfur Centers; FD
for ferredoxin; and FNR for Ferredoxin NADP oxido
Reductase (FNR). Three major protein complexes are
involved in running the "Z" scheme: (1) Photosystem II; (2) Cytochrome
bf complex (containing Cytb6;
FeS; and Cytf ) and (3) Photosystem I. The
diagram does not show where and how ATP is made.
For a description of how the Z Scheme operates,
click here.
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