Functional Changes of Lysozyme by Conjugating with Carboxymethyl Dextran.
Hen egg lysozyme-carboxymethyl dextran (HEL-CMD) conjugate was prepared by using water-soluble carbodiimide as a model protein-acidic polysaccharide conjugate for improving the protein function. An acid-amide bond between HEL and CMD was confirmed by SDS-PAGE, isoelectric focusing and IR spectra. The molar ratio of CMD to HEL in the conjugate was 1:1. The isoelectric point of the conjugate was 5.5-6.0, which is much lower than that of HEL. Spectroscopic studies suggested that the conformation around the Trp residue had not changed but the α-helix content had decreased to about 1/3 that for native HEL. The conjugate maintained about 60% of the enzymatic activity of native HEL at 40-60°C, while it was about 1.4 times as active as native HEL at 4°C and 80°C. The conjugate was more stable to proteolysis than native HEL. The denaturation temperature of the conjugate was about 73°C, which is almost the same as that of native HEL. However, the enthalpy for denaturation of the conjugate was about 1/3 that of native HEL, which corresponds to the decrease in α-helix content.
a Department of Applied Biological Science , Faculty of Agriculture, Tokyo University of Agriculture and Technology , Tokyo 183 , Japan.
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Hattori
a Department of Applied Biological Science , Faculty of Agriculture, Tokyo University of Agriculture and Technology , Tokyo 183 , Japan.
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Imamura
a Department of Applied Biological Science , Faculty of Agriculture, Tokyo University of Agriculture and Technology , Tokyo 183 , Japan.
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Nagasawa
a Department of Applied Biological Science , Faculty of Agriculture, Tokyo University of Agriculture and Technology , Tokyo 183 , Japan.
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Takahashi