The enzyme introduces an unusual trans double bond at carbon 3 of a palmitoyl group attached to the sn-2 position of glycerolipids. The enzyme from the plant Arabidopsis thaliana is specific for palmitate in phosphatidylglycerol. The enzyme from tobacco can also accept oleate and ¦Á-linolenate if present at the sn-2 position of phosphatidylglycerol [1].