(a) Desaturases and hydrolysis in fatly acid biosynthesis. An important example of rational redesign of natural biocatalysts is the re­engineering of membrane-bound di-iron enzymes having activities like hydroxylase, epoxidase, acetylenase and conjugase activities during, fatty-acid biosynthesis in plants. A comparison of sequences of five related oleate desaturases with two hydroxylases allowed identification of seven positions, which were conserved in five desaturases but differed from equivalent positions in two hydroxylases.
Reciprocal amino acid changes between a desaturase and hydroxylase at the seven identified sites brought about pronounced shifts in the ratio of desaturase to hydroxylase activity. It was shown that four amino-acid substitutions were sufficient to convert a desaturase to hydroxylase and six substitutions converted a hydroxylase to a desaturase.

(b) Catalytic activity with 2-ethonyl-coenzyme A hydratase/isomerase superfamily. A comparison of sequence and structures of various dehalogenases form this family suggested that all active sites can be derived from a single ancestral active site, which provides (i) CoA binding, (ii) an oxyanion pocket and (iii) a chamber, where substrate and catalytic groups are positioned. It was shown that placement of one or more polar residues at the chamber using site-directed mutagenesis can alter its properties and genetic/chemical diversity. For instance, eight amino acid substitutions from crotonyl hydratase onto 4-chlorobenzoyl­CoA-dehalogenase, conferred upon the latter the ability to catalyse hydration of crotonyl-CoA.