Glucose isomerases having altered substrate specificity

A glucose isomerase which is a modified form of a naturally occurring glucose isomerase having a determinable three dimensional structural wherein said modification comprises substituting a different amino acid from that occurring at at least one position of said naturally occurring glucose isomerase, wherein said position is identified by:

• selecting all residues and crystallographically assigned water molecules as they exist in said three-dimensional structure which have at least one atom within a sphere of 4 angstroms surrounding the atoms of a substrate bound in the active site of said glucose isomerase and residues which are in van der Waal's contact with said residues and water molecules thus selected, to obtain ia first list of residues and water molecules;
• discarding from said list of residues and water molecules those that are involved in catalysis, cofactor binding and essential intersubunit interactions to obtain a reduced list of residues and water molecules;
• discarding from said reduced list of residues and water molecules those that interfere with the structural roles of those resides discarded from said first list to obtain a twice-reduced list of residues and water molecules,
• wherein said position to be substituted is selected from among those residues on said twice-reduced list.