Attaching a single polymer chain to a specific site away from the active center of the protein has less impact on protein activity compared with random attachments. In practice, attaching a single polymer chain can be used to adjust chemical properties of the therapeutic protein. For example, conjugation of a single chain of the hydrophilic polyethylene glycol (PEG) can increase the hydrodynamic radius of the protein conjugate by 5-10 fold. Attachment to PEG was mainly achieved by covalent conjugation via the grafting to strategy, targeting chemo-selective anchor groups. Other polymers, such as oligosaccharides and polypeptides, offer different properties to the enzymes attached to them.