Ubiquitin Proteasome Activity Measurement in Total Plant Extracts.

The fine-tuned balance of protein level, conformation and location within the cell is vital for the dynamic changes required for a cell to respond to a given stimulus. This requires the regulated turnover of damaged or short-lived proteins through the ubiquitin proteasome system (UPS). Thus, the protease activity of the proteasome is adjusted to meet the current demands of protein degradation via the UPS within the cell. We describe the adaptation of an intramolecular quenched fluorescence assay utilizing substrate-mimic peptides for the measurement of proteasome activity in total plant extracts. The peptide substrates contain donor-quencher pairs that flank the scissile bond. Following cleavage, the increase in dequenched donor emission of the product is subsequently measured over time and used to calculate the relative proteasome activity.