Ca2+-activated protease activity in frog sciatic nerve: characterization and effect on rapidly transported axonal...

Area of Science:

• Neurobiology
• Enzymology

Background:

• Protease activity is crucial for neuronal function and protein turnover.
• Rapid axonal transport (AXT) delivers essential proteins to nerve terminals.

Purpose of the Study:

• To investigate protease activity within the frog sciatic nerve.
• To characterize the properties and substrates of proteases involved in degrading axonal transport proteins.

Main Methods:

• Measuring TCA-soluble radioactivity from 3H-labeled proteins transported via AXT or from ganglionic proteins.
• Assessing protease activity in nerve homogenates and desheathed nerves under varying pH and calcium conditions.
• Utilizing a calcium ionophore (X-537 A) and elevated calcium concentrations to study enzyme activation.

Main Results:

• Protease activity showed peaks at pH 5 and pH 8, with Ca2+ (≥100 µM) stimulating the pH 8 peak.
• The pH 8 protease activity was inhibited by a sulfhydryl reagent but unaffected by ATP.
• Elevated Ca2+ and ionophore treatment activated protease activity in desheathed nerves, correlating with increased Ca2+ flux.
• The protease degraded both rapidly transported and soluble ganglionic proteins, indicating broad substrate specificity.

Conclusions:

• Frog sciatic nerves contain a soluble, Ca2+-activated protease within axons that degrades rapidly transported proteins.
• This protease possesses broad substrate specificity, also degrading soluble ganglionic proteins.
• The characterized protease system offers a valuable model for studying protease activity under diverse physiological conditions.