Pitfalls in invertebrate proteasome assays

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• The ubiquitin-proteasome system is crucial for intracellular protein turnover.
• Invertebrate proteasomes are increasingly studied for their roles in physiological processes.
• Standard proteasome activity assays can be unreliable due to non-proteasomal enzyme interference.

Purpose of the Study:

• To investigate the reliability of proteasome activity assays across different invertebrate taxa.
• To quantify the contribution of proteasomal versus non-proteasomal proteolytic activity.
• To highlight the necessity of using specific inhibitors in proteasome research.

Main Methods:

• Utilized a proteasome-specific inhibitor, epoxomicin.
• Assayed chymotrypsin-like activity using a model polypeptide substrate.
• Compared proteasomal and non-proteasomal activities in various invertebrate tissues and yeast.

Main Results:

• Proteasomal activity dominated in crustacean muscle and hemocytes.
• In yeast, proteasomes accounted for approximately 90% of total proteolytic activity.
• Bivalve tissues showed a lower proteasomal contribution (20-60%) to total proteolytic activity.

Conclusions:

• Proteasome activity assays can yield erroneous data if non-proteasomal activities are not accounted for.
• The proportion of proteasomal activity varies significantly among invertebrate taxa.
• Specific inhibitors are essential for accurate interpretation of proteasome function in crude extracts.