Development of Specific Inhibitors of CYP707A, a Key Enzyme in the Catabolism of Abscisic Acid

UDP-glucose pyrophosphorylase (UGPase) is a key enzyme producing UDP-glucose, which is involved in an array of metabolic pathways concerned with, among other functions, the synthesis of sucrose and cellulose. An Arabidopsis thaliana UGPase-encoding gene, Ugp, was profoundly up-regulated by feeding sucrose to the excised leaves and by an exposure of plants to low temperature (5°C). The UGPase activity and its protein content also increased under conditions of sucrose feeding and exposure to cold. The sucrose effect on Ugp was apparently specific and was mimicked by exposure of dark-adapted leaves to light. Drought and O2 deficiency had some down-regulating effects on expression of Ugp. The sugar-signalling pathway for Ugp regulation was independent of hexokinase, as was found by using transgenic plants with increased and decreased expression of the corresponding gene. Subjecting mutants deficient in abscisic acid (ABA) to cold stress conditions had no effect on Ugp expression profiles. Okadaic acid was a powerful inhibitor of Ugp expression, whereas it up-regulated the gene encoding sucrose synthase (Sus1), indicating distinct transduction pathways in transmitting the sugar signal for the two genes in A. thaliana. We suggest that Ugp gene expression is mediated via a hexokinase-independent and ABA-insensitive pathway that involves an okadaic acid-responsive protein phosphatase. The data point towards Ugp as a possible regulatory entity that is closely involved in the homoeostatic readjustment of plant responses to environmental signals.

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Ppm1, a novel polyprenol monophosphomannose synthase from Mycobacterium tuberculosis

Biochemical Journal ◽

10.1042/bj20020107 ◽

2002 ◽

Vol 365 (2) ◽

pp. 441-450 ◽

Cited By ~ 82

Author(s):

Sudagar S. GURCHA ◽

Alain R. BAULARD ◽

Laurent KREMER ◽

Camille LOCHT ◽

D.Branch MOODY ◽

...

Keyword(s):

Mycobacterium Tuberculosis ◽

Gene Disruption ◽

Domain Architecture ◽

In Vitro Assay ◽

Diverse Range ◽

Vitro Assay ◽

Attractive Candidate ◽

Key Enzyme ◽

Specific Inhibitors

Dolichol monophosphomannose (DPM) is an ever-present donor of mannose (Man) in various eukaryotic glycosylation processes. Intriguingly, the related polyprenol monophosphomannose (PPM) is involved in the biosynthesis of lipomannan and lipoarabinomanan, key bacterial factors termed modulins that are found in mycobacteria. Based on similarities to known DPM synthases, we have identified and characterized the PPM synthase of Mycobacterium tuberculosis, now termed Mt-Ppm1. In the present study, we demonstrate that Mt-Ppm1 possesses an unusual two-domain architecture, by which the second domain is sufficient for PPM synthesis. However, when overexpressed separately in mycobacteria, domain 1 of Mt-Ppm1 appears to increase the synthesis of PPM. Interestingly, other mycobacteria such as M. smegmatis, M. avium and M. leprae produce two distinct proteins, which are similar to the two domains found in Mt-Ppm1. Using an in vitro assay, we also demonstrate that Mt-Ppm1 transfers Man from GDP-Man to a structurally diverse range of lipid monophosphate acceptors. The identification of the PPM synthase as a key enzyme in lipoarabinomannan biosynthesis now provides an attractive candidate for gene disruption to generate mutants for subsequent immunological studies. PPM synthase can also be exploited as a target for specific inhibitors of M. tuberculosis.

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Role of class II phosphoinositide 3-kinase in cell signalling

Biochemical Society Transactions ◽

10.1042/bst0350211 ◽

2007 ◽

Vol 35 (2) ◽

pp. 211-214 ◽

Cited By ~ 61

Author(s):

M. Falasca ◽

T. Maffucci

Keyword(s):

Cell Signalling ◽

Class Ii ◽

Key Enzyme ◽

Phosphoinositide 3 Kinase ◽

Specific Inhibitors

Although it is now well established that PI3K (phosphoinositide 3-kinase) is a key enzyme in several intracellular processes, there are still relatively few reports that precisely identify the specific isoforms of PI3K actually involved in such events. The lack of specific inhibitors has made it particularly difficult to address the physiological roles of some isoforms, such as the members of class II. As a consequence, there is still relatively little understanding of the role of these enzymes and the question about the intracellular role of these isoforms still waits for more answers.

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Arabidopsis CYP707As Encode (+)-Abscisic Acid 8′-Hydroxylase, a Key Enzyme in the Oxidative Catabolism of Abscisic Acid

PLANT PHYSIOLOGY ◽

10.1104/pp.103.037614 ◽

2004 ◽

Vol 134 (4) ◽

pp. 1439-1449 ◽

Cited By ~ 323

Author(s):

Shigeki Saito ◽

Nobuhiro Hirai ◽

Chiaki Matsumoto ◽

Hajime Ohigashi ◽

Daisaku Ohta ◽

...

Keyword(s):

Abscisic Acid ◽

Key Enzyme

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Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. V. Inhibition by Tungstate and its Removal by Cinchonine shows that Xanthoxal is Oxidised by a Molybdo-Aldehyde Oxidase

Functional Plant Biology ◽

10.1071/pp96060 ◽

1997 ◽

Vol 24 (6) ◽

pp. 727 ◽

Cited By ~ 12

Author(s):

H-S. Lee ◽

B. V. Milborrow

Keyword(s):

Abscisic Acid ◽

Aldehyde Oxidase ◽

Inhibitory Effect ◽

Biosynthetic Pathways ◽

Free System ◽

Cell Free System ◽

Avocado Fruit ◽

A Cell ◽

Specific Inhibitors

A cell-free preparation from avocado fruit incorporates [14C]mevalonate into ABA. A number of specific inhibitors have been used to probe the system and tungstate ions at 100 µM reduce the 14C in ABA by 80% The inhibitory effect was overcome by the alkaloid cinchonine (2000 µM) which binds tungstate strongly and selectively. More 14C from mevalonate was present in xanthoxal (4600 dpm), less in ABA (340 dpm) when the cell-free system was inhibited by tungstate (100 µM) than in controls (1810 dpm in xanthoxal, 1200 dpm in ABA), which shows that xanthoxal is the substrate for the aldehyde oxidase. Xanthoxic acid, therefore, is the next intermediate and AB-aldehyde is not a normal precursor. The potential for using the tungstate/cinchonine reaction to probe other biosynthetic pathways which require a molybdate ion is discussed.

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