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Drug
Enzyme
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Query: EC:4.1.1.32 (
phosphoenolpyruvate carboxykinase
)
4,204
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
Cells associated with veins of petioles of C(3) tobacco possess high activities of the decarboxylase enzymes required in C(4) photosynthesis. It is not clear whether this is the case in other C(3) species, nor whether these enzymes provide precursors for specific biosynthetic pathways. Here, we investigate the activity of C(4) acid decarboxylases in the mid-vein of Arabidopsis, identify regulatory regions sufficient for this activity, and determine the impact of removing individual isoforms of each protein on mid-vein metabolite profiles. This showed that radiolabelled malate and bicarbonate fed to the xylem stream were incorporated into soluble and insoluble material in the mid-vein of Arabidopsis leaves. Compared with the leaf lamina, mid-veins possessed high activities of NADP-dependent malic enzyme (NADP-ME), NAD-dependent malic enzyme (NAD-ME) and
phosphoenolpyruvate carboxykinase
(
PEPCK
). Transcripts derived from both NAD-ME, one PCK and two of the four NADP-ME genes were detectable in these veinal cells. The promoters of each decarboxylase gene were sufficient for expression in mid-veins. Analysis of insertional mutants revealed that cytosolic NADP-
ME2
is responsible for 80% of NADP-ME activity in mid-veins. Removing individual decarboxylases affected the abundance of amino acids derived from pyruvate and phosphoenolpyruvate. Reducing cytosolic NADP-ME activity preferentially affected the sugar content, whereas abolishing NAD-ME affected both the amino acid and the glucosamine content of mid-veins.
...
PMID:C acid decarboxylases required for C photosynthesis are active in the mid-vein of the C species Arabidopsis thaliana, and are important in sugar and amino acid metabolism. 1980 80
Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that exploits a temporal CO
2
pump with nocturnal CO
2
uptake and concentration to reduce photorespiration, improve water-use efficiency (WUE), and optimize the adaptability of plants to hotter and drier climates. Introducing the CAM photosynthetic machinery into C
3
(or C
4
) photosynthesis plants (CAM Biodesign) represents a potentially breakthrough strategy for improving WUE while maintaining high productivity. To optimize the success of CAM Biodesign approaches, the functional analysis of individual C
4
metabolism cycle genes is necessary to identify the essential genes for robust CAM pathway introduction. Here, we isolated and analyzed the subcellular localizations of 13 enzymes and regulatory proteins of the C
4
metabolism cycle of CAM from the common ice plant in stably transformed
Arabidopsis thaliana
. Six components of the carboxylation module were analyzed including beta-carbonic anhydrase (
McBCA2
),
phosphoenolpyruvate carboxylase
(
McPEPC1
),
phosphoenolpyruvate carboxylase
kinase (
McPPCK1
), NAD-dependent malate dehydrogenase (
McNAD-MDH1
,
McNAD-MDH2
), and NADP-dependent malate dehydrogenase (
McNADP-MDH1
). In addition, seven components of the decarboxylation module were analyzed including NAD-dependent malic enzyme (
McNAD-ME1
,
McNAD-
ME2
), NADP-dependent malic enzyme (
McNADP-ME1
,
NADP-
ME2
), pyruvate, orthophosphate dikinase (
McPPDK
), pyruvate, orthophosphate dikinase-regulatory protein (
McPPDK-RP
), and
phosphoenolpyruvate carboxykinase
(
McPEPCK
). Ectopic overexpression of most C
4
-metabolism cycle components resulted in increased rosette diameter, leaf area, and leaf fresh weight of
A. thaliana
except for
McNADP-MDH1
,
McPPDK-RP
, and
McPEPCK.
Overexpression of most carboxylation module components resulted in increased stomatal conductance and dawn/dusk titratable acidity (TA) as an indirect measure of organic acid (mainly malate) accumulation in
A. thaliana
. In contrast, overexpression of the decarboxylating malic enzymes reduced stomatal conductance and TA. This comprehensive study provides fundamental insights into the relative functional contributions of each of the individual components of the core C
4
-metabolism cycle of CAM and represents a critical first step in laying the foundation for CAM Biodesign.
...
PMID:Laying the Foundation for Crassulacean Acid Metabolism (CAM) Biodesign: Expression of the C
4
Metabolism Cycle Genes of CAM in
Arabidopsis
. 3080 70
