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beta-Galactosidase from Bacillus stearothermophilus.

R E Goodman, D M Pederson

Canadian Journal of Microbiology

|June 1, 1976

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Thermophilic bacilli constitutively produce beta-galactosidase, an enzyme with optimal activity at 65°C. This enzyme exhibits stability at 50°C but is sensitive to heat, though protein can offer some protection.

Area of Science:

Enzymology
Microbiology
Biochemistry

Background:

Several thermophilic aerobic spore-forming bacilli strains constitutively synthesize beta-galactosidase (EC 3.2.1.23).
The constitutive nature of this enzyme production is not attributed to a temperature-sensitive repressor.

Purpose of the Study:

To characterize the biochemical and kinetic properties of beta-galactosidase from a thermophilic bacillus strain.
To investigate the enzyme's stability and the effect of protective agents on thermal inactivation.

Main Methods:

Enzyme assays were performed using cell-free extracts.
Kinetic parameters (Km, Ki) were determined.
Thermal stability and inactivation kinetics were studied.
Molecular weight was estimated using disc gel electrophoresis.

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Main Results:

The enzyme exhibits a pH optimum between 6.0 and 6.4 with sharp acid-side dependence.
Optimal temperature is 65°C, with distinct Arrhenius activation energies below and above 47°C.
Km values for lactose and 9-nitrophenyl-beta-D-galactopyranoside were determined at 55°C.
Strong product inhibition by galactose was observed (Ki = 2.5 x 10⁻³ M).
The enzyme is stable at 50°C but rapidly inactivated at 60°C, with bovine serum albumin offering partial protection.

Conclusions:

The beta-galactosidase from this thermophilic bacillus strain possesses specific kinetic and stability characteristics.
Understanding these properties is crucial for applications involving thermophilic enzymes.
Protein presence can mitigate thermal inactivation, suggesting potential stabilization strategies.