Chemical modification of horseradish peroxidase with several methoxypolyethylene glycols

The chemical modification of epsilon-NH2 lysine residues of horseradish peroxidase (E.C. 1.11.1.7) with several mPEG was carried out. The modified enzymes were studied through chromatographic and electrophoretic methods; the extent of mPEG linking was determined using H-1-NMR. Peroxidase, modified with mPEG ranging from 350 to 5000, activated with 4-nitrophenylchloroformate (mPEGpn), showed a better thermal stability than the native, but there was no correlation between the length of the polymer adduct and the improvement. The enzyme was modified with mPEG (5000) activated by cyanuric chloride (mPEGcc). The number of modified lysine increased, but the thermal behavior of mPEGcc peroxidase was similar to those of mPEGpn enzymes. In all cases, the modification did not markedly change the stability in organic solvents.