Pressure-induced inactivation of sarcoplasmic reticulum adenosine triphosphatase during high-speed centrifugation

Sarcoplasmic reticulum vesicles were found to be highly sensitive to high-speed centrifugation in metal-deprived mediums at low temperature (4 degrees C). The irreversible modifications induced were easily detected from observation of the environment-sensitive spectrum of an iodoacetamide spin-label bound to the ATPase. Centrifugation also resulted in vesicle aggregation and inhibition of calcium transport, ATPase activity, and phosphoenzyme formation. These denaturation-like phenomena were prevented in the presence of sucrose, or by nucleotide binding, or, again, by cation binding to the ATPase high-affinity calcium binding sites and were only present when centrifugation was performed at low temperature. The crucial parameter during this process was found to be the hydrostatic pressure which developed in the centrifuge tube. SR vesicles exposed to 800 bars in a pressure bomb displayed the same features. It is suggested that irreversible denaturation takes place after one or both of the two following well-documented effects of pressure: a rise in the lipid order/disorder transition temperature or dissociation of the oligomeric structure of the calcium pump.