We are interested in constructing a model for the substrate-bindingsiteof fattyacidelongase-13-ketoacylCoAsynthase (FAE1 KCS),the enzyme responsible forproductionof very long chain fatty acids of plant seed thaliana andBrassica napusFAE1 KCS enzymes are highly homo-logous but the seed oil content of these plants suggests that their substrate specificities differ with respect to acyl chain length.