Journal of Microbiology and Biotechnology

The Korean Society for Microbiology and Biotechnology (한국미생물·생명공학회)
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The Importance of Tyr-475 and Glu-506 in $\beta$-Galactosidase from L. lactis ssp.lactis 7962

  • Yang, Eun-Ju (Department of Food and Nutrition, Chosun University) ;
  • Lee, Jung-Min (Department of Food Science and Technology, Seoul National University) ;
  • Lee, Hyong-Joo (Department of Food Science and Technology, Seoul National University) ;
  • Kim, Jeong-Hwan (Division of Applied Life Science Graduate School, Gyeongsang National University) ;
  • Chung, Dae-Kyun (Institute and Department of Genetic Engineering, Kyung Hee University) ;
  • Lee, Jong-Hoon (Department of Foods and Biotechnology, Kyunggi University) ;
  • Chang, Hae-Choon (Department of Food and Nutrition, Chosun University)
  • Published : 2003.02.01
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Abstract

The secondary and tertiary structures of ${\beta}$-galactosidase from L. lactis ssp. lactis 7962 were designed using Nnpredict and Sybyl version 6.3. By using site-directed mutagenesis, the mutated enzymes, Tyr-475-phe and Glu-506-Asp, were generated based on the structural modeling of L. lactis ssp. lactis 7962. The enzymes Tyr.-475-Phe and Glu-506-Asp had <$1\%$ of the activity of the native enzyme with ONPG as substrate. The $V_{max}$ values of the mutated enzymes were greatly reduced (1,800~40,000-1314) compared with the value for the native ${\beta}$-galactosidase. However, the $K_m$ values of Tyr-475-Phe and Glu-506-Asp with ONPG, PNPG, PNPF, and PNPA were not significantly different from those of the native enzyme. The results obtained support the suggestion that Tyr-475 and Glu-506 constitute very important parts of the catalytic machinery of the ${\beta}$-galactosidase.

Keywords

References

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