A modified enzyme molecule, comprising a modified transglutaminase enzyme molecule with a modification that increases a perceived volume of said modified enzyme molecule, wherein said modification is selected from the group consisting of a modification that increases an actual size of said modified enzyme molecule a modification that increases a hydrodynamic volume of said modified enzyme molecule and a modification that modifies an electrostatic charge of said modified enzyme molecule to be of opposite sign to a net charge of said substrate polymer by changing the isoelectric point (pi) of said modified enzyme in comparison to unmodified enzyme wherein said increase in said perceived volume prevents excessive cross-linking of a substrate by said modified enzyme molecule, wherein said excessive cross-linking leads to a reduction in mechanical properties of cross-linked substrate, or results in reduced elution of said modified enzyme molecule from said cross-linked substrate.
