A highly active soluble diacylglycerol synthesizing system from developing rapeseed,Brassica napus L. |
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Authors: | Denis J Murphy |
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Affiliation: | (1) Department of Botany, University of Durham, DH1 3LE Durham, UK |
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Abstract: | The subcellular distribution of the enzymes of triacylglycerol biosynthesis has been studied in developing oilseed rape. All
in vitro enzymatic activities from oleoyl-CoA to triacylglycerol were sufficient to account for the known rate of oleate deposition
in triacylglycerol in vivo. The enzymatic activities from oleoyl-CoA to diacylglycerol preferentially were localized in a
150,000 g supernatant fraction, while the diacylglycerol acyl-transferase mostly was associated with the microsomal (20,000
g pellet and 150,000 g pellet) and oil-body fractions. The soluble (150,000 g supernantant) fraction rapidly incorporated
oleate from 1-14C]oleoyl-CoA into diacylglycerol with rates of 40 nm min−1 g−1 FW at 20 μM oleoyl-CoA. The pH optimum was 7.5–9.0, and normal saturation kinetics were seen with oleoyl-CoA; the S0.5 was about 32 μM. Exogenous acyl acceptors, such as glycerol 3-phosphate, lysophosphatidic acid and lysophosphatidylcholine
stimulated oleate incorporation into diacylglycerol. The detergents Triton X-100 and sodium cholate inhibited diacylglycerol
formation at concentrations in the region of their critical micellar concentration, while n-octyl-β,D-glyco-pyranoside had
no effect, even at high concentration. The significance of these findings for the mechanism of oil-body formation in developing
oilseeds is discussed. |
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