DESATURATION AND RELATED MODIFICATIONS OF FATTY-ACIDS

Desaturation of a fatty acid first involves the enzymatic removal of a hydrogen from a methylene group in an acyl chain, a highly energy-dem anding step that requires an activated oxygen intermediate. Two types of desaturases have been identified, one soluble and the other membran e-bound, that have different consensus motifs. Database searching for these motifs reveals that these enzymes belong to two distinct multifu nctional classes, each of which includes desaturases, hydroxylases, an d epoxidases that act on fatty acids or other substrates. The soluble class has a consensus motif consisting of carboxylates and histidines that coordinate an active site diiron cluster. The integral membrane c lass contains a different consensus motif composed of histidines. Bioc hemical and structural similarities between the integral membrane enzy mes suggest that this class also uses a diiron cluster for catalysis. Soluble and membrane enzymes have been successfully re-engineered for substrate specificity and reaction outcome. It is anticipated that rat ional design of these enzymes will result in new and desired activitie s that may form the basis for improved oil crops.