beta-Galactosidase from Aspergillus niger. Separation and characterization of three multiple forms

Area of Science:

• Enzymology
• Biochemistry
• Microbial Biotechnology

Background:

• Beta-galactosidase (EC 3.2.1.23) is crucial for lactose hydrolysis.
• Enzyme multiplicity can arise from post-translational modifications, impacting function.
• Aspergillus niger is a significant source of industrial enzymes.

Purpose of the Study:

• To purify and characterize multiple forms of beta-galactosidase from Aspergillus niger.
• To investigate the structural and functional basis of enzyme multiplicity.
• To assess the potential physiological relevance of observed differences.

Main Methods:

• Enzyme purification using molecular sieving, ion-exchange, and hydrophobic chromatography.
• Characterization of enzyme forms including molecular weight, isoelectric point, and pH optima.
• Amino acid and carbohydrate composition analysis, kinetic studies (Km, Vmax).

Main Results:

• Three beta-galactosidase forms were isolated, constituting 83%, 8%, and 9% of total activity.
• Enzyme forms are glycoproteins with distinct molecular weights (124-173 kDa) and carbohydrate content (12.5-29%).
• All forms exhibited acidic pH optima (2.5-4.0), heat stability up to 60°C, and comparable kinetic parameters.

Conclusions:

• Multiplicity of Aspergillus niger beta-galactosidase is primarily attributed to variations in neutral carbohydrate content.
• Observed differences in enzyme forms are unlikely to be physiologically significant.
• The biological role of this multiplicity may be linked to glycosylation patterns, common in microbial enzymes.