Enzymes conjugation with polyethylene glycol

Chemical modification, particularly succinylation, or coupling to polyglycols, can also increase the plasma half-life of enzymes. Conjugation with polyethylene glycol [PEG H(OCH2CH2)nOH] has successfully been employed to stabilize and protect several therapeutic enzymes. Such modification, for example, increases the plasma half-life of superoxide dismutase from 5 h to over 30 h. PEG-coupled asparaginase was approved for general medical use by the FDA in 1994. 

Beckman, J. S., Minor, R. F., White, C. W., Repine, J. E., Rosen, G. M and Freeman, B. A. (1988) Superoxide dismutase and catalase conjugated with polyethylene glycole increase endothelial enzyme activity and oxidant resistance. J. Biol. Chem. 263, 6884-6892. 

About 150 lipid molecules were present per 1 of enzyme. It was used to esterify 1-phenylethanol with lauric acid in isooctane, giving 95% conversion in 2 h. A lipid-coated lipase has also been used to esterify lauric acid with glycerol in sc carbon dioxide with 90% conversion.98 Catalase with less than 5% of its surface amino groups modified by the nonionic surfactant 9.7 had a higher activity in 1,1,1-trichloroethane than when the enzyme was conjugated with polyethylene glycol.99... 

The improvement of its activity and stability has been approach by the use of GE tools (see Refs. [398] and [399], respectively). A process drawback is the fact that the oxidation of hydrophobic compounds in an organic solvent becomes limited by substrate partition between the active site of the enzyme and the bulk solvent [398], To provide the biocatalyst soluble with a hydrophobic active site access, keeping its solubility in organic solvents, a double chemical modification on horse heart cytochrome c has been performed [400,401], First, to increase the active-site hydrophobicity, a methyl esterification on the heme propionates was performed. Then, polyethylene glycol (PEG) was used for a surface modification of the protein, yielding a protein-polymer conjugates that are soluble in organic solvents. 

Abuchowski, A., Kazo, G.M., Verhoest Jr., C.R., van Es, T., Kafkewitz, D., Nucci, M.L., Viau, A.T., and Davis, F.F. (1984) Cancer therapy with chemically modified enzymes. Anti-tumor properties of polyethylene glycol asparaginase conjugates. Cancer Biochem. Biophys. 7, 175-186. 

Another mode of enzyme replacement therapy is periodic administration of a polyethylene glycol-modified form of bovine intestinal ADA by intramuscular injection. The modified enzyme, which is prepared by conjugating polyethylene glycol with purified ADA (PEG-ADA), possesses a longer half-life as well as reduced immuno-genicity. As a consequence of this treatment, the correction... 

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