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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)
Publication Information
Journal of Microbiology and Biotechnology / v.13, no.1, 2003 , pp. 134-138 More about this Journal
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
${\beta}$-Galactosidase; tyrosine-475; glutamic acid- 506; L. lactis 7962; substrate binding site;
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Times Cited By KSCI : 3  (Citation Analysis)
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