beta-Galactosidase from Bacillus stearothermophilus.
Several strains of thermophilic aerobic spore-forming bacilli synthesize beta-galactosidase (EC 3.2.1.23) constitutively. The constitutivity is apparently not the result of a temperature-sensitive repressor. The beta-galactosidase from one strain, investigated in cell-free extracts, has a pH optimum between 6.0 and 6.4 and a very sharp pH dependence on the acid side of its optimum. The optimum temperature for this enzyme is 65 degrees C and the Arrhenius activation energy is about 24 kcal/mol below 47 degrees C and 16 kcal/mol above that temperature. At 55 degrees C the Km is 0.11 M for lactose and 9.8 X 10(-3) M for 9-nitrophenyl-beta-D-galactopyranoside. The enzyme is strongly product-inhibited by galactose (Ki equals 2.5 X 10(-3) M). It is relatively stable at 50 degrees C, losing only half of its activity after 20 days at this temperature. At 60 degrees C more than 60% of the activity is lost in 10 min. However, the enzyme is protected somewhat against thermal inactivation by protein, and in the presence of 4 mg/ml of bovine serum albumin the enzyme is only 18% inactivated in 10 min at 60 degrees C. Its molecular weight, estimated by disc gel electrophoresis, is 215 000.
D000332:Aerobiosis; D002241:Carbohydrates / Q000494:pharmacology; D002474:Cell-Free System; D004794:Enzyme Repression; D005690:Galactose / Q000494:pharmacology; D005696:Galactosidases / Q000096:biosynthesis / Q000378:metabolism; D001411:Geobacillus stearothermophilus / Q000201:enzymology* / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D009598:Nitrophenylgalactosides / Q000378:metabolism; D013171:Spores, Bacterial / Q000254:growth & development; D013696:Temperature
D002241:Carbohydrates; D009598:Nitrophenylgalactosides; D005696:Galactosidases; D005690:Galactose