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KMID : 0545120030130010134
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Journal of Microbiology and Biotechnology
2003 Volume.13 No. 1 p.134 ~ p.138
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The Importance of Tyr-475 and Glu-506 in β-Galactosidase from L. lactis ssp. lactis 7962
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YANG, EUN JU
LEE, JUNG MIN/LEE, HYONG JOO/KIM, JEONG HWAN/CHUNG, DAE KYUN/LEE, JONG HOON/CHANG, HAE CHOON
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Abstract
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The secondary and tertiary structures of β-galatosidase 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 (1,8000~40,000-fold) compared with the value for the native β-galatosidase. However, the K_m values of Tyr-475-Phe and Glu-506-Asp with ONPG, PNPG, PNPE, 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 β-galatosidase.
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KEYWORD
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