EFFECTS OF PRESSURE ON ACTOMYOSIN SYSTEMS

The interactions of actin with myosin, heavy meromyosin, and subfragment 1 were investigated under pressure from 1 atm up to 4000 kg/cm2. The results obtained by the change in the intensity of transmitted light through a pressure cell showed that, in the absence of adenosine triphosphate, turbid solutions of myosin B, actomyosin, and heavy actomeromyosin became transparent with increasing pressure finally to give constant intensities of transmitted light at ca. 2000 kg/cm2, indicating some change in the state of molecules in a solution under pressure. When dissociation of actomyosin into actin and myosin under pressure is assumed, pressure effects on actomyosin should be the same as on the individual component. Flowever, experiments for denaturation of F-actin, heavy meromyosin, and heavy actomeromyosin by pressure demonstrated that heavy meromyosin plus pressure-treated F-actin (at 3500 kg/cm2) had less adenosine triphosphatase activity than F-actin plus pressuretreated heavy meromyosin and pressure-treated heavy actomeromyosin, suggesting that heavy meromyosin protected denaturation of F-actin. In the presence of adenosine triphosphate, high magnesium adenosine triphosphatase activity of heavy actomeromyosin, and actosubfragment 1 decreased sharply to magnesium adenosine triphosphatase of heavy meromyosin, and subfragment 1 in the pressure range from 1 atm to 700 kg/cm2. Calcium-activated adenosine triphosphatase of heavy actomeromyosin and actosubfragment 1, on the other hand, showed an increase in activity by pressure, the increase which was due to the pressure effect for adenosine triphosphatase of heavy meromyosin, and subfragment 1. Summarizing those results, the pressure effects on actomyosin systems are accounted for in terms of depolymerization or dissociation of protein components, and adenosine triphosphate plays an important role in interactions of actin and heavy meromyosin. © 1969, American Chemical Society. All rights reserved.