The bgIX gene located at 47.8 min on the Escherichia coll chromosome encodes a periplasmic -glucosidase

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Abstract
A new Escherichia coli gene, bgIX, encoding a β-D-glucosidase (EC 3.2.1.21) has been characterized. The bgIX gene is located adjacent to the dld gene at 47.8 min or 2225 kb on the E. coli chromosome. The sequence of a 2.6 kb DNA fragment from this region revealed a large open reading frame encoding a protein of 765 amino acids. The BgIX protein was purified from the peripiasm, and amino-terminal sequencing suggests that the mature protein is derived from cleavage of a 20 residue signal peptide. A search of the sequence databases revealed that BgIX is a member of a large family of β-glucosidases from a variety of bacteria and fungi, and the plant Arabidopsis thaliana. It differs from the other four E. coli phospho-β-glucosidases in sequence and in its periplasmic rather than cytoplasmic location. The BgIX enzyme has a Km of 18 ± 1 mM and a Vmax of 3 ± 0.7 μmol min-1 for the colorimetric substrate o-nitrophenyl β-D-glucopyranoside.

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