Hydrostatic pressure effects on rabbit and echinoderm myosin ATPase.

When saturated with ATP, sea cucumber myosin hydrolyzes ATP about 15 times more slowly than rabbit myosin, as expected from the slower contraction time of the muscle. The Arrhenius plots coincide at low temperatures, but only the rabbit plot changes slope at higher temperatures. This unexpected change in slope apparently results from the use of Verona1 buffer. At high substrate concentrations in Verona1 buffer, the enzymatic activities of the two proteins depend identically on calcium ion and on pH. The two myosins are equally inhibited by pressure at low pH and activated at high, suggesting that structural features common to the two enzymes are responsible for pressure sensitivity and its pH dependence.