Abstract
While intracellular proline accumulation in response to various stress conditions has been investigated in great detail, the biochemistry and physiological relevance of proline degradation in plants is much less understood. Moreover, the second and last step in proline catabolism, the oxidation of δ(1)-pyrroline-5-carboxylic acid (P5C) to glutamate, is shared with arginine catabolism. Little information is available to date concerning the regulatory mechanisms coordinating these two pathways. Expression of the gene coding for P5C dehydrogenase was analyzed in rice by real-time PCR either following the exogenous supply of amino acids of the glutamate family, or under hyperosmotic stress conditions. The rice enzyme was heterologously expressed in E. coli, and the affinity-purified protein was thoroughly characterized with respect to structural and functional properties. A tetrameric oligomerization state was observed in size exclusion chromatography, which suggests a structure of the plant enzyme different from that shown for the bacterial P5C dehydrogenases structurally characterized to date. Kinetic analysis accounted for a preferential use of NAD(+) as the electron acceptor. Cations were found to modulate enzyme activity, whereas anion effects were negligible. Several metal ions were inhibitory in the micromolar range. Interestingly, arginine also inhibited the enzyme at higher concentrations, with a mechanism of uncompetitive type with respect to P5C. This implies that millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate. Results are discussed in view of the involvement of the enzyme in either proline or arginine catabolism.
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Claims 7
Claim · model-written summary
Rice P5C dehydrogenase was observed as a tetramer.
- Taxon
- rice
Oryza sativat0 - Gene
- P5C dehydrogenasee1
- Outcome
- tetrameric oligomerization statee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“A tetrameric oligomerization state was observed in size exclusion chromatography”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
Claim · model-written summary
The rice enzyme preferentially used NAD(+) as electron acceptor.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee1
- Outcome
- preferential use of NAD(+)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“Kinetic analysis accounted for a preferential use of NAD(+) as the electron acceptor.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
Claim · model-written summary
Cations modulated rice enzyme activity.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee1
- Compound
- Cationse0
- Outcome
- enzyme activitye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“Cations were found to modulate enzyme activity, whereas anion effects were negligible.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
Claim · model-written summary
Anions had negligible effects on rice enzyme activity.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee1
- Compound
- anione0
- Outcome
- enzyme activitye0
- Direction
- negligiblee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“Cations were found to modulate enzyme activity, whereas anion effects were negligible.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
Claim · model-written summary
Several metal ions inhibited rice enzyme activity in the micromolar range.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee1
- Compound
- metal ionse0
- Outcome
- enzyme activitye2
- Direction
- inhibitorye0
- Qualifier
- micromolar rangee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“Several metal ions were inhibitory in the micromolar range.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
e2“Cations were found to modulate enzyme activity, whereas anion effects were negligible.”
Claim · model-written summary
Arginine inhibited the rice enzyme at higher concentrations through an uncompetitive mechanism relative to P5C.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee1
- Compound
- argininee0
- Outcome
- inhibited the enzymee0
- Direction
- inhibitede0
- Qualifier
- higher concentrations, with a mechanism of uncompetitive type with respect to P5Ce0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“arginine also inhibited the enzyme at higher concentrations, with a mechanism of uncompetitive type with respect to P5C.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
Claim · model-written summary
Millimolar arginine was inferred to increase rice P5C dehydrogenase affinity for its substrate.
- Taxon
- riceOryza sativat0
- Gene
- P5C dehydrogenasee0
- Compound
- argininee0
- Outcome
- affinity of P5C dehydrogenase toward its specific substratee0
- Direction
- increasee0
- Qualifier
- millimolar levelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rice δ1-pyrroline-5-carboxylate dehydrogenase”
e0“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”
e1“millimolar levels of arginine would increase the affinity of P5C dehydrogenase toward its specific substrate.”