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SBB 4101 PLANT BIOCHEMISTRY
SUMMARY: PLANT FATTY ACID & ISOPRENOID SYNTHESIS
Done by,
SHANMUGAPRAKASHAM S/O SELVAMANI (UK16456)
BACHELOR OF SCIENCE (BIOLOGICAL SCIENCES)
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PLANT FATTY ACID SYNTHESIS:
Beitlenmiller, D. P., Roughan, G. & Ohlrogge, J. B. 1992.
Regulation of plant fatty acid
biosynthesis.Plant Physiology. 100: 923 930.
The study was done as continues to evaluate factors involved in
plant fatty acid biosynthesis as
previous study was on the in vivo acyl acyl carier proteins
(ACP) involved in fatty acid
biosynthesis. In this study, to evaluate role of other factors
of substrates and cofactors involved,
coenzyme A (CoA), acetyl- and malonyl-CoA were examined. De vovo
fatty acid biosynthesis
occurs in the plastids and catalyzed by a series of enzymes and
mediated by ACP. The precursor
substrate of the pathway is acetyl-CoA and melonyl-CoA. From
this study, it was found that the
major form of CoA in chloroplast and whole leaves is acetyl-CoA
and they are also do not differ
greatly in light and dark. The transfer of acetyl- or melonyl
from CoA to ACP is catalyzed by a
transacylase enzyme.
Examination of the changes in pool sizes of intermediates in a
pathway in this study has provided
evidence for the metabolic regulation. Regulatory steps are
characterized by increases in their
substrate concentration and decreases in product concentration
when the flux through the
pathway is reduced. Results from this study support the role of
acetyl-CoA carboxylase in
regulation of plastid fatty acid biosynthesis. Malonyl-CoA
levels were undetectable in dark
incubated chloroplasts, but rose manyfold in the light and
increased further when fatty acid
synthesis was stimulated in the light by Triton X-100. The level
of acetyl-CoA was reduced
concomitantly with the increases in malonyl- CoA. Thus, the
changes in both the substrate and
product pools of the acetyl-CoA carboxylase reaction provide
direct evidence for its role indetermining the flux through the
fatty acid biosynthetic pathway. Thus, the study provides
sufficient evidence of the regulation and role played by
acetyl-CoA carboxylase in plant fatty
acid biosynthesis.
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PLANT ISOPRENOID SYNTHESIS:
Calisto, B. M., Perez-gil, J., Bergua, M., Querol-audi, J.,
Fita, I. & Imperial, S. 2007.Biosynthesis of isoprenoids in
plant: structure of the 2c-methyl-D-erithrytol 2,4-
cyclodiphosphate synthase from Arabidopsis thaliana. Comparison
with the bacterial
enzymes.Protein Science. 16: 2082 2088.
The study was conducted to construct crystal structure of the
2C-methyl-D-erythritol 2,4-
cyclodiphosphate (MCS) synthase from Arabidopsis thaliana.
Isopentenyl diphosphate (IPP)
and its isomer dimethylallyl diphosphate (DMAPP) are the
five-carbon precursors of isoprenoids
biosynthesis. IPP was identified to be synthesized from
acetyl-CoA via mevalonic acid pathway
in yeast and animals. There is an alternative pathway for
biosynthesis of IPP which was
identified later in baceteria. Plants use both pathways. MCS
converts 4-diphosphocytidyl
2C-methyl-D-erythritol 2-phosphate (CDP-MEP) to 2Cmethyl D -
erythritol 2,4
cyclodiphosphate (MECDP) and cytidine-5-monophosphate (CMP). The
first crystal structure
from a plant MCS enzyme has been determined, in complex with a
CMP molecule. The
molecular trimeric organization and the overall structure of
subunits, in particular the
arrangement of the catalytically essential residues and the
active site, are closely related to the
ones from the known structures of the bacterial enzymes. Main
differences between the plant and
the bacterial MCS structures concentrate in the cavity that
exists between subunits along the
molecular threefold axis and involve residues that are highly
conserved among plants. These
differences suggest that the binding of isoprenoid
diphosphate-like molecules in the cavity of the
plant MCS enzymes would not occur, contrary to what had been
demonstrated for some bacterial
enzymes.
