Phanerochaete chrysosporium beta-Glucosidases: Induction, Cellular Localization, and Physical Characterization

Area of Science:

• Biochemistry
• Enzymology
• Microbial Physiology

Background:

• Phanerochaete chrysosporium is a white-rot fungus known for its ligninolytic capabilities.
• Beta-glucosidases play a crucial role in cellulose degradation by hydrolyzing cellobiose into glucose.
• Understanding the regulation and properties of beta-glucosidases is vital for biotechnological applications, such as biofuel production.

Purpose of the Study:

• To characterize the extracellular and intracellular beta-glucosidases produced by Phanerochaete chrysosporium.
• To investigate the induction and repression mechanisms governing the synthesis of these enzymes.
• To determine the kinetic and physical properties of both enzyme forms.

Main Methods:

• Enzyme assays using p-nitrophenyl-beta-glucoside and cellobiose as substrates.
• Determination of enzyme kinetics (Km, Ki) under varying substrate and inhibitor concentrations.
• Measurement of molecular weight, optimal temperature, activation energy, and pH optima.
• Investigation of enzyme induction and repression using cellulose, cellobiose, and glucose in culture media.
• Assessment of cycloheximide's effect on enzyme induction.

Main Results:

• Phanerochaete chrysosporium produces distinct extracellular and intracellular beta-glucosidases.
• Extracellular beta-glucosidase is induced by cellulose and competitively inhibited by glucose (Ki = 5.0 x 10^-4 M).
• Intracellular soluble beta-glucosidase is induced by cellobiose, unaffected by glucose, and its induction is sensitive to cycloheximide.
• Both enzymes exhibit optimal activity at 45°C, with similar activation energies.
• pH optima differ: approximately 7.0 for intracellular and 5.5 for extracellular enzymes.

Conclusions:

• The regulation of beta-glucosidase synthesis in Phanerochaete chrysosporium is complex, involving distinct mechanisms for extracellular and intracellular forms.
• The extracellular enzyme's repression by glucose suggests a feedback mechanism to prevent futile cycling.
• The characterization of these enzymes provides valuable data for optimizing their use in lignocellulosic biomass degradation.