and prolactin the enzyme may have an active site e g a catalytic triad which may consist of ser asp and his the parent enzymes may be selected so as to have identical residues in the active site three dimensional structure is meant to be a known crystal structure or a model structure the 3d structure of each polypeptide may already be known or it may be modeled using the known 3d structures of one or more polypeptides with a high sequence homology using an appropriate modeling program such as homology modeller or nest the 3d model may be optimized using molecular dynamics simulation as available e g in charmm or namd the optimization may particularly be done in a water environment e g a box or sphere the homology modeller and charmm software is available from accelrys inc 9685 scranton road san diego calif 92121 3752 usa accelrys com the nest software is distributed free of charge at trantor bioc columbia edu programs jackal index html the namd software is available at ks uiuc edu research namd the 3d models may be structurally aligned by methods known in the art the structural alignment may be done by use of known software in the structurally aligned models pairs of residues from different sequences are considered to be aligned when they are located close to each other the following software may be used in the case of enzymes having an active site the structural alignment may be a superimposition of the structures based on the deviations of heavy atoms i e non hydrogen atoms in the active sites e g by minimizing the sum of squares.