Characterization of NADP-dependent malic enzyme from developing castor oil seed endosperm.
Metabolic pathways sequestered within the leucoplast of developing oilseeds ensure a balanced supply of substrates and cofactors for fatty acid biosynthesis. NADP-dependent malic enzyme (NADP-ME) may be important in supplying both carbon and NADPH for fatty acid biosynthesis in the developing endosperm of the oilseed Ricinus communis. NADP-ME was purified 5160-fold to a specific activity of 18.2 U/mg protein. NADP-ME is a homotetramer with a native mass of 254 kDa and a subunit size of approximately 63 kDa. Effectors of castor NADP-ME are typical of the NADP-malic enzymes, with the exception of acetyl-CoA and its derivatives, which were found to act as activators. This is consistent with a regulatory role for these molecules during fatty acid biosynthesis in vivo. NADP-ME was found to have maximal activity at stage 7 of endosperm development, coincident with maximal lipid accumulation.
Shearer
Heather L
HL
Department of Biology, Queen's University, Kingston, Ont., Canada K7L 3N6. hshearer@uoguelph.ca
Turpin
David H
DH
Dennis
David T
DT
D015153:Blotting, Western; D002368:Castor Oil; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008970:Molecular Weight; D009249:NADP / Q000378:metabolism*; D012639:Seeds / Q000201:enzymology* / Q000254:growth & development; D013696:Temperature
D007527:Isoenzymes; D009249:NADP; D002368:Castor Oil; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)