Effects of a high-pressure treatment on the activity and structure of rabbit muscle proteasome

The effects were assessed of high hydrostatic pressure on the activity and structure of rabbit skeletal muscle proteasome. The pressure effects on the activity were measured by the amount of fluorometric products released from synthetic substrates under pressure and from fluorescein isothiocyanate (FITC)-labeled casein after releasing the pressure. The effects on the structure were measured by fluorescene spectroscopy under pressure, and by circular dichroism (CD) spectroscopy and surface hydrophobicity after releasing the pressure. The optimal pressure for the hydrolyzing activity of synthetic peptides was 50 MPa. The degradation of FITC-labeled casein increased linearly with increasing pressure applied up to 200 MPa, and then markedly decreased up to at 400 MPa. The changes in the tertiary structure detected by fluorometric measurement were irreversible, whereas the changes in the secondary structure were small compared with those by heat treatment. The pressure-induced activation of proteasome therefore seems to have been due to a little unfolding of the active sites of proteasome.