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Activation of cathepsin D by polyanionic compounds

S Watabe¹, T Ikeda, N Yago

¹Radioisotope Laboratory, Faculty of Agriculture, Yamaguchi University, Japan.

Biochemistry and Molecular Biology International

|July 1, 1996

Summary

Tripolyphosphate activates the enzyme cathepsin D by altering its charge, increasing its affinity for substrates. This polyanionic compound reduces electrostatic repulsion, enhancing enzyme activity.

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Area of Science:

Biochemistry
Enzymology

Background:

Cathepsin D is a key aspartic protease involved in various cellular processes.
Polyanionic compounds are known to modulate enzyme activity through various mechanisms.

Purpose of the Study:

To investigate the mechanism by which polyanionic compounds, specifically tripolyphosphate, activate cathepsin D.
To elucidate the role of electrostatic interactions in this activation process.

Main Methods:

Enzyme kinetics assays were performed using porcine cathepsin D and bovine serum albumin as substrate.
Electrophoretic mobility studies were conducted to assess changes in enzyme charge at varying tripolyphosphate concentrations.

Main Results:

Tripolyphosphate decreased the Michaelis constant (Km) for cathepsin D without affecting the maximum velocity (VMAX).
Half-maximal activation occurred at 0.2 mM tripolyphosphate.
Increased tripolyphosphate concentration reduced the electrophoretic mobility of cathepsin D, indicating charge neutralization.

Conclusions:

Tripolyphosphate activates cathepsin D by reducing electrostatic repulsion between the enzyme and its substrate.
The observed activation is attributed to the cancellation of positive charges on cathepsin D by the polyanion.

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