Evidence that oleoyl-CoA and ATP-dependent elongations coexist in rapeseed(Brassica napus L.)

The elongation of different substrates was studied using several subcellula r fractions from Brassica napus rapeseed. In the presence of malonyl-CoA, N ADH and NADPH, very-long-chain fatty acid (VLCFA) synthesis was observed fr om either oleoyl-CoA (acyl-CoA elongation) or endogenous primers (ATP-depen dent elongation). No activity was detected using oleic acid as precursor. A cyl-CoA and ATP-dependent elongation activities were mainly associated with the 15 000 g/25 min membrane fraction. Reverse-phase TLC analysis showed t hat the proportions of fatty acids synthesized by these activities were dif ferent. Acyl-CoA elongation increased up to 60 mu M oleoyl-CoA, and ATP-dep endent elongation was maximum at 1 mM ATP. Both activities increased with m alonyl-CoA concentration (up to 200 mu M). Under all conditions tested, acy l-CoA elongation was higher than ATP-dependent elongation, and, in the pres ence of both ATP and oleoyl-CoA, the elongation activity was always lower. ATP strongly inhibited acyl-CoA elongation, whereas ATP-dependent elongatio n was slightly stimulated by low oleoyl-CoA concentrations (up to 150 mu M) and decreased in the presence of higher concentrations. CoA (up to 150 mu M) had no effect on the ATP-dependent elongation, whereas it inhibited the acyl-CoA elongation. These marked differences strongly support the presence in maturing rapeseed of two different elongating activities differently mo dulated by ATP and oleoyl-CoA.