Score: 3.00 |
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| Title: Phosphoenolpyruvate carboxylase protein kinase from developing castor oil seeds : partial purification , characterization , and reversible control by photosynthate supply .
| | Author: Murmu J Plaxton WC | | Journal: Planta Citation: V : 226 P : 1299-310 Year: 2007 Type: MEDLINE | | Literature: oryza Field: abstract Doc ID: pub17624549 Accession (PMID): 17624549 | | Abstract: Phosphoenolpyruvate carboxylase ( PEPC , EC 4 . 1 . 1 . 31 ) protein kinase ( PPCK ) was purified approximately 1 , 500-fold from developing castor oil seeds ( COS ) .
Gel filtration and immunoblotting with anti- ( rice PPCK2 ) -immune serum indicated that this Ca2+-insensitive PPCK exists as a 31-kDa monomer .
COS PPCK-mediated rephosphorylation of the 107-kDa subunit ( p107 ) of COS PEPC1 ( Km = 2 . 2 microM ) activated PEPC1 by approximately 80% when assayed under suboptimal conditions ( pH 7 . 3 , 0 . 2 mM PEP , and 0 . 125 mM malate ) .
COS PPCK displayed remarkable selectivity for phosphorylating COS PEPC1 ( relative to tobacco , sorghum , or maize PEPCs ) , exhibited a broad pH-activity optima of approximately pH 8 . 5 , and at pH 7 . 3 was activated 40-65% by 1 mM PEP , or 10 mM Gln or Asn , but inhibited 65% by 10 mM L-malate .
The possible control of COS PPCK by disulfide-dithiol interconversion was suggested by its rapid inactivation and subsequent reactivation when incubated with oxidized glutathione and then dithiothreitol .
In vitro PPCK activity correlated with in vivo p107 phosphorylation status , with both peaking in mid-cotyledon to full-cotyledon developing COS .
Notably , PPCK activity and p107 phosphorylation of developing COS were eliminated following pod excision or prolonged darkness of intact plants .
Both effects were fully reversed 12 h following reillumination of darkened plants .
These results implicate a direct relationship between the up-regulation of COS PPCK and p107 phosphorylation during the recommencement of photosynthate delivery from illuminated leaves to the non-photosynthetic COS .
Overall , the results support the hypothesis that PEPC and PPCK participate in the control of photosynthate partitioning into C-skeletons needed as precursors for key biosynthetic pathways of developing COS .
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[ Sen. 3, subscore: 2.00 ]: COS PPCK-mediated rephosphorylation of the 107-kDa subunit ( p107 ) of COS PEPC1 ( Km = 2 . 2 microM ) activated PEPC1 by approximately 80% when assayed under suboptimal conditions ( pH 7 . 3 , 0 . 2 mM PEP , and 0 . 125 mM malate ) .
[ Sen. 4, subscore: 1.00 ]: COS PPCK displayed remarkable selectivity for phosphorylating COS PEPC1 ( relative to tobacco , sorghum , or maize PEPCs ) , exhibited a broad pH-activity optima of approximately pH 8 . 5 , and at pH 7 . 3 was activated 40-65% by 1 mM PEP , or 10 mM Gln or Asn , but inhibited 65% by 10 mM L-malate .
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