Enzymic properties of thermopsin

Area of Science:

• Biochemistry
• Enzymology
• Extremophile Biology

Background:

• Thermopsin is a thermostable acid protease isolated from the extremophilic archaeon Sulfolobus acidocaldarius.
• Understanding protease specificity and kinetics is crucial for enzyme applications and biological function elucidation.

Purpose of the Study:

• To determine the substrate specificity of thermopsin.
• To characterize the kinetic properties and inhibition patterns of thermopsin.
• To investigate the role of its active site and temperature dependence.

Main Methods:

• Incubation of thermopsin with oxidized insulin B chain and a synthetic substrate.
• Peptide isolation, identification, and cleavage site determination.
• Enzyme kinetics assays, inhibition studies with pepstatin and other inhibitors, and temperature dependence analysis.

Main Results:

• Thermopsin hydrolyzes bonds adjacent to large hydrophobic residues, similar to pepsin.
• Optimal activity observed at 75°C and pH 2, with specific kinetic parameters (Km, kcat).
• Pepstatin competitively inhibits thermopsin, while other aspartic protease inhibitors show weak or non-specific effects; thiol modification reagents are ineffective.

Conclusions:

• Thermopsin exhibits pepsin-like specificity but possesses a distinct active site structure.
• Its activity is highly temperature-dependent, peaking near the organism's optimal growth temperature.
• The enzyme's properties suggest adaptation for function in high-temperature, high-substrate environments.