Mechanism of Stimulation of the Calcium Adenosinetriphosphatase by Jasmone

Abstract

The ATPase activity of the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum is increased ca. 3-fold at 25 degrees C and pH 7.2 by jasmone at a concentration of 100 microM, concentrations above 10 mM resulting 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 at pH 6.0 than at pH 7.2. The effects of jasmone on the ATPase are highly specific. Jasmone has no effect on the E1<-->E2 equilibrium constant for the ATPase or on Ca2+ binding. The rate of phosphorylation by ATP is unaffected by jasmone, and only small effects are seen on the reaction of the phosphorylated ATPase with ADP. Jasmone does, however, increase the rate of dephosphorylation by a factor of 2 and the rate of dissociation of Ca2+ from the phosphorylated ATPase by a factor of 3. Jasmone decreases the level of phosphorylation of the ATPase by P(i) in the absence of Ca2+ consistent with a decrease in the equilibrium constant E2P(i)Mg<-->E2PMg. Reconstitution of the ATPase with dimyristoleoylphosphatidylcholine decreases the stoichiometry of Ca2+ binding from the usual 2:1 to 1:1. Unlike other hydrophobic molecules, jasmone failed to reverse this effect. Further, jasmone had very similar effects on the activity of the ATPase reconstituted with either dimyristoleoylphosphatidylcholine or dioleoylphosphatidylcholine, whereas other hydrophobic molecules caused a much greater stimulation of activity for the ATPase reconstituted with the short-chain lipid.

Methyl Jasmonate-Induced Stimulation of Sarcoplasmic Reticulum Ca2+-ATPase Affects Contractile Responses in Rat Slow-Twitch Skeletal Muscle

“…These results are similar to those previously reported on the ATPase activity of the purified Ca 2ϩ -ATPase from rabbit fast skeletal muscle (Starling et al, 1994), except that in our experiments, methyl jasmonate concentrations were 100-fold lower. The fact that comparable effects were obtained for calcium loading in both types of muscle suggests that the application of methyl jasmonate resulted in an increase of ATPase activity in slow muscle, with a maximum response at 100 M.…”

“…Thus, the present results (Fig. 1b), showing a bell-shaped relationship between loading rate and methyl jasmonate effects, are in line with previous findings obtained in the presence of jasmone, menthone, menthol, and methyl jasmonate (Starling et al, 1994).…”

“…In previous studies, the effect of jasmone and methyl jasmonate on SR Ca 2ϩ -ATPase was demonstrated in a series of experiments conducted on the purified Ca 2ϩ -ATPase from rabbit fasttwitch skeletal muscles (Starling et al, 1994). The purpose of the present study was to confirm these results in slow mammalian skeletal muscle.…”

“…Biochemical investigations have recently shown that jasmone, menthone, menthol, and methyl jasmonate are highly selective stimulators of the SR Ca 2ϩ -ATPase in mammalian skeletal muscle, whereas they have no effect on the properties of the phospholipid bilayer (Starling et al, 1994). Surprisingly, no study has investigated the effects of these substances on skeletal muscle contraction.…”

“…Methyl jasmonate, a linolenic acid-derived cyclopentanone-base, has also been shown to trigger defense reactions in various plants and to be produced in response to wounds and elicitor treatment (Rickauer et al, 1997). Because methyl jasmonate can stimulate ATP-dependent Ca 2ϩ activity of the purified Ca 2ϩ -ATPase from rabbit fasttwitch skeletal muscle (Starling et al, 1994), it seemed of interest to estimate the specificity of methyl jasmonate effects on Ca 2ϩ loading by the SR. Chemically skinned slow muscle fibers (soleus) were chosen for these experiments, as sarcolemmal functions can be eliminated and Ca 2ϩ mobilization greatly simplified.…”