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=LDR 03981cam a22003493i 4500
=001 4127175
=005 20170321141247.0
=006 m\\f\\d\\\\
=008 130101s2013\\kina\\smb\\000\0\eng\d
=040 \$aCaOKQ$beng$erda$cCaOKQ
=100 1$aHill, Allyson.$edissertant
=245 10$aSerine-451 phosphorylation of bacterial-type phosphoenolpyruvate carboxylase by a calcium-dependent protein kinase links calcium signaling with anaplerotic pathway control in developing castor oil seeds /$cby Allyson Tarah Hill.
=264 \1$aKingston, Ont. :$b[publisher not identified],$cc2013.
=264 \4$c©2013.
=300 \$axi, 94 leaves :$billustrations (some colour)
=336 \$atext$btxt$2rdacontent
=337 \$acomputer$bc$2rdamedia
=338 \$aonline resource$bcr$2rdacarrier
=347 \$atext file$bPDF$2rda
=502 \$aMaster$bBiology$cQueen's University$d2013
=504 \$aIncludes bibliographical references (leaves 74-82)
=520 3$aPhosphoenolpyruvate (PEP) carboxylase (PEPC) is a tightly controlled enzyme situated at a pivotal branchpoint of plant C-metabolism. Two physically and kinetically distinct oligomeric classes of PEPC exist in the endosperm of developing castor oil seeds (COS). Class-1 PEPC is a typical homotetramer composed of 107-kDa plant-type PEPC (PTPC) subunits, whereas the 910-kDa Class-2 PEPC hetero-octameric complex arises from a tight interaction between Class-1 PEPC and distantly related 118-kDa bacterial-type PEPC (BTPC) subunits. BTPC functions as both a catalytic and regulatory subunit of the allosterically-desensitized Class-2 PEPC, which has been hypothesized to support massive PEP-flux to malate for leucoplast fatty acid synthesis. Previous studies established that BTPC: (i) subunits of COS Class-2 PEPC are subject to inhibitory phosphorylation in vivo, and (ii) at Ser425 and Ser451 within an intrinsically disordered region. This study focuses on characterization of the COS protein kinase (BTPC-K) that phosphorylates BTPC at Ser451. BTPC-K, having a native molecular mass of 63 kDa, was purified ~500-fold from developing COS endosperm. Its activity was absolutely dependent upon the presence of Ca2+ (Ka= 2.7 [mu] M) and millimolar Mg2+. BTPC-K phosphorylated BTPC subunits of Class-2 PEPC strictly at Ser451 (Km= 1.1 [mu] M), as well as histone type III-S (Km= 1.7 [mu] M) but did not phosphorylate a BTPC S451D phosphomimetic mutant, native COS PTPC or sucrose synthase, or α-casein. BTPC-K displayed a broad pH-activity optima of pH 7.3, a Km for Mg2+-ATP of 6.6 [mu] M, and marked inhibition by 3-P-glycerate and PEP. The possible control of BTPC-K by disulfide-dithiol interconversion was suggested by its rapid inactivation and subsequent reactivation when incubated with oxidized glutathione and then dithiothreitol. BTPC-K activity was insensitive to exogenous calmodulin, but potently inhibited by 100 [mu] M trifluoperazine (a calmodulin antagonist). BTPC-K-mediated Ser451 phosphorylation of BTPC subunits of Class-2 PEPC inhibited BTPC activity by ~50% when assayed under suboptimal conditions (pH 7.3, 1 mM PEP with 10 mM L-malate). Overall the results of this study have led to the hypothesis that in vivo phosphorylation of COS BTPC at Ser451 is mediated by a dedicated calcium-dependent protein kinase (CDPK).
=538 \$aMode of access: World Wide Web.
=540 \$aThis publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
=653 \$aPEPC.
=653 \$aCastor oil seed.
=653 \$aCalcium-dependent protein kinase.
=653 \$aBacterial-type PEPC.
=710 2$aQueen's University (Kingston, Ont.).$tTheses (Queen's University (Kingston, Ont.))
=710 2$aQueen's University (Kingston, Ont.).$bDepartment of Biology.
=830 \0$aCanadian theses.
=948 \$ac:sb

Record File: b6b27b459de3cea868d8b8665da68c82.mrc