Causes of the Production of Multiple Forms of β-Galactosidase byBacillus circulans

The Discoidin Domain ofBacillus circulansβ-Galactosidase Plays an Essential Role in Repressing Galactooligosaccharide Production

“…[27][28][29][30][31][32][33][34] It has been reported that the presence of the DS domain enhances the hydrolytic activity of various glycosidases due to high interaction between the substrate and enzyme molecules [28][29][30] but knowledge of the functions of the DS domain in -galactosidase 12,17) is limited. The objective of this study was to elucidate the role of the DS domain in the repression of GOS production.…”

“…-Galactosidase activity was assayed using 8 mM o-NPG and 143 mM lactose as substrates in the assay buffer at 40 C by a method used in a previous study. 12,24) The final enzyme concentration was 2-4 mg/mL, unless otherwise noted. One unit with o-NPG as substrate (U o-NPG ) was defined as the amount of protein required to produce 1 mmol of o-NP per minute at 40 C at pH 6, and 1 unit with lactose as substrate (U lactose ), as the amount of protein required to produce 1 mmol of D-glucose under the same conditions, as reported previously.…”

“…One unit with o-NPG as substrate (U o-NPG ) was defined as the amount of protein required to produce 1 mmol of o-NP per minute at 40 C at pH 6, and 1 unit with lactose as substrate (U lactose ), as the amount of protein required to produce 1 mmol of D-glucose under the same conditions, as reported previously. 12,24) Protein concentrations were determined by the BCA method using a BCA Protein Assay Reagent Kit (Pierce Chemical, Rockford, IL) with BSA as standard.…”

“…[1][2][3][4] Hence a number of attempts to isolate -galactosidases with high transgalactosylation activities from various microorganisms have been reported, [5][6][7][8][9][10][11][12][13] and genes that encode -galactosidases, [13][14][15][16][17][18][19][20][21][22][23][24] including those of B. circulans ATCC 31382, 13,24) have been cloned. However, the lack of a crystal structure as well as a lack of knowledge of the multimeric and monomeric structures of a number of high molecular weight -galactosidases, except for Escherichia coli -galactosidase, 25) has been a drawback to developing an understanding of the mechanism of transgalactosylation.…”

“…However, the lack of a crystal structure as well as a lack of knowledge of the multimeric and monomeric structures of a number of high molecular weight -galactosidases, except for Escherichia coli -galactosidase, 25) has been a drawback to developing an understanding of the mechanism of transgalactosylation. 25,26) We recently have isolated and characterized agalactosidase from Bacillus circulans ATCC 31382 12) and cloned the gene (DDBJ accession no. AB605256).…”