Transcript Prezentace aplikace PowerPoint

SO4
S
S
2
2
2–
SO4
=
2–
S
+ ATP + 8
–
e
+8
+
H
=
+ 4 H2O + AMP + PPi
APS sulfotransferase, using APS as a sulfuryl
donor, transfers sulfate to an acceptor thiol
compound, possibly glutathione.
The resulting organic thiosulfonate is reduced
to thiosulfide by a ferredoxin-dependent
thiosulfonate reductase.
APS is first phosphorylated to PAPS by APS
kinase.
PAPS reductase then produces sulfite by
using electrons donated from thioredoxin.
Sulfite reductase then completes the
reduction to sulfide by using electrons from
ferredoxin.
major endproduct of the reductive
sulfate assimilation, glutathione, is the
major nonprotein thiol in plants (its
milimolar concentrations far exceed the
micromolar conc. of cysteine)
involved in the storage and long distance
transport of reduced sulfur, in signal
transduction pathways, in scavenging
active oxygen species, in detoxifying
xenobiotics and serving as a substrate for
phytochelatin synthesis
Two phytochelatin molecules [(gama-Glu-Cys)2Gly] coordinated
with an ion of cadmium. By binding toxic heavy metal ions,
phytochelatins remove them from the cellular machinery.
A model for the mechanism of CdS mineralization
and sequestration in plant cells mediated by
phytochelatins
(A) The phytoplankton-climate connection.
Phytoplankton-produced DMSP
(dimethylsulfoniopropionate) is broken down
by bacteria to DMS (dimethyl sulfide) and
acrylate. DMS volatilizes and is oxidized to
DMSO and to sulfate, which nucleates water
droplets, leading to cloud formation.
(B) Sulfate is returned to the sea dissolved in rain. Because
cloud cover reduces the growth of phytoplankton and is
accompanied by atmospheric cooling, phytoplankton have
been proposed to serve as a homeostatic climate regulation
mechanism.
Dimethylsulfoniopropionate (DMSP) has many roles, e.g.
osmoprotectant, cryoprotectant repellant against
planctonic herbivores