MECHANISM OF STIMULATION OF THE CALCIUM ADENOSINE-TRIPHOSPHATASE BY JASMONE

The ATPase activity of the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum is increased ca. 3-fold at 25 degrees C and pH 7.2 by jasmo ne at a concentration of 100 mu M, concentrations above 10 mM resultin g in reduced stimulation. Stimulation by methyl jasmonate, menthol, or menthone requires much higher concentrations. Effects of jasmone are much less marked at 37 degrees C than at 25 degrees C, and much higher concentrations of jasmone are required to stimulate ATPase activity a t pH 6.0 than at pH 7.2. The effects of jasmone on the ATPase are high ly specific. Jasmone has no effect on the E1 reversible arrow E2 equil ibrium constant for the ATPase or on Ca2+ binding. The rate of phospho rylation by ATP is unaffected by jasmone, and only small effects are s een on the reaction of the phosphorylated ATPase with ADP. Jasmone doe s, however, increase the rate of dephosphorylation by a factor of 2 an d the rate of dissociation of Ca2+ from the phosphorylated ATPase by a factor of 3. Jasmone decreases the level of phosphorylation of the AT Pase by P-i in the absence of Ca2+ consistent with a decrease in the e quilibrium constant E2P(i)Mg reversible arrow E2PMg. Reconstitution of the ATPase with dimyristoleoylphosphatidylcholine decreases the stoic hiometry of Ca2+ binding from the usual 2:1 to 1:1. Unlike other hydro phobic molecules, jasmone failed to reverse this effect. Further, jasm one had very similar effects on the activity of the ATPase reconstitut ed with either dimyristoleoylphosphatidylcholine or dioleoylphosphatid ylcholine, whereas other hydrophobic molecules caused a much greater s timulation of activity for the ATPase reconstituted with the short-cha in lipid.