Metabolic control analysis of de novo sunflower fatty acid biosynthesis

We have obtained a simulation of the final steps of de novo fatty acid bios ynthesis in sunflower control line RHA-274, For this simulation, we have us ed data from the evolution of fatty acids during seed formation and from th e biochemical characterization of beta -keto-acyl-ACP synthetase II (FASII) , stearoyl-ACP desaturase (SAD) and acyl-ACP thioesterase activities and th e program GEPASI (based on the metabolic control-analysis theory). When phy siological data from high- and medium-stearic acid mutants seed development were used with this model the predicted changes in SAD and TE were very si milar to those actually found in the biochemical characterization of these mutants. However, the model had to be modified when results from high-palmi tic mutants, accumulating unusual fatty acids like palmitoleic, asclepic an d palmitolinoleic acids, were used. The emerging model, that fits all of ou r results, predicts the existence of a dynamic channelling between the FASI I complex and SAD, that channelling being responsible for the alternative p athway starting with the desaturation of palmitic acid by the stearoyl-ACP desaturase. This channelling is consistent with our previous results. For i nstance, the determination of SAD activity on sunflower seed crude extracts only rendered oleic acid when the stearic acid used as a substrate was obt ained from a KASII assay, but not when the stearic acid came from in vitro synthesis using acyl-ACP synthetase from Escherichia coli. This theoretical approximation will be very useful in predicting the evolution of the syste m when introducing new or modified activities; similar approximations in ot her oil-seed crops could be of great interest.