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Substitutions for Cys-472 and His-509 at the Active Site of $\beta$-Galactosidase from Lactococcus lactis ssp. lactis 7962 Cause Large Decreases in Enzyme Activity  

Chung Hye-Young (Department of Food and Nutrition, Chosun University)
Yang Eun-Ju (Department of Food and Nutrition, Chosun University)
Chang Hae-Choon (Department of Food and Nutrition, Chosun University)
Publication Information
Journal of Microbiology and Biotechnology / v.16, no.8, 2006 , pp. 1325-1329 More about this Journal
Abstract
Structural modeling of $\beta$-galactosidase from L. lactis ssp. lactis 7962 has shown that the residues Cys-472 and His-509 are located in the wall of the active-site cavity. To examine the functions of Cys-472 and His-509, we generated five site-specific mutants: Cys-472-Ser, Cys-472-Thr, Cys-472-Met, His-509-Asn, and His-509-Phe. $\beta$-Galactosidase substituted at Cys-472 with Met or His-509 with Phe had <3% of the activity of the native enzyme when assayed using ONPG as substrate. The other mutants Cys-472-Ser, Cys-472-Thr, and His-509-Asn had ca. 10-15% of the native enzyme activity. The V$_max$ values of the five mutated enzymes were lower (60-7,000-fold) than that of native enzyme. These results show that the catalytic ability of $\beta$-galactosidase is significantly affected by mutations at Cys-472 or His-509.
Keywords
$\beta$-Galactosidase; Cys-472; His-509; L. lactis 7962;
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Times Cited By Web Of Science : 2  (Related Records In Web of Science)
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