Mutagenesis of the borage A6 fatty acid desaturase

The consensus sequence of the third histidine box of a range of A,, A6, An and sphingolipid desatu-rases differs from that of the membrane-bound non-fusion A' ' and A15 desaturases in the presence of glutamine instead of histidine. We have used site-directed mutagenesis to determine the im-portance of glutamine and other residues of the third histidine box and created a chimaeric enzyme to determine the ability of the Cyt 6, fusion domain from the plant sphingolipid desaturase to sub-stitute for the endogenous domain of the A, desaturase