Comparison of the effects of phospholamban and jasmone on the calcium pump of cardiac sarcoplasmic reticulum. Evidence for modulation by phospholamban of both Ca2+ affinity and Vmax (Ca) of calcium transport.

Antipenko AY, Spielman AI, Kirchberger MA.

Source

Department of Physiology and Biophysics, Mount Sinai School of Medicine of the City University of New York, New York, New York 10029-6574, USA.

Abstract

Regulation of the calcium pump of the cardiac sarcoplasmic reticulum by phosphorylation/dephosphorylation of phospholamban is central to the inotropic and lusitropic effects of beta-adrenergic agonists on the heart. In order to study the mechanism of this regulation, we first obtained purified ruthenium red-insensitive microsomes enriched in sarcoplasmic reticulum membranes. The kinetics of microsomal Ca2+ uptake after phospholamban phosphorylation or trypsin treatment, which cleaves the inhibitory cytoplasmic domain of phospholamban, were then compared with those in the presence of jasmone, whose effects on the kinetics of fast skeletal muscle Ca2+-ATPase are largely known. All three treatments increased Vmax (Ca) at 25 degrees C and millimolar ATP; phosphorylation and trypsin decreased the Km (Ca), while jasmone increased it. Trypsin and jasmone increased the rate of E2P decomposition 1.8- and 3. 0-fold, respectively. The effects of phospholamban phosphorylation and jasmone on the Ca2+-ATPase activity paralleled their effects on Ca2+ uptake. Our data demonstrate that phospholamban regulates E2P decomposition in addition to the known increase in the rate of a conformational change in the Ca2+-ATPase upon binding the first of two Ca2+. These steps in the catalytic cycle of the Ca2+-ATPase may contribute to or account for phospholamban’s effects on both Vmax (Ca) and Km (Ca), whose relative magnitude may vary under different experimental and, presumably, physiological conditions.

2. Biochem J. 1996 Nov 15;320 ( Pt 1):101-5.

Stimulation of the Ca(2+)-ATPase of sarcoplasmic reticulum by disulfiram.

Starling AP, East JM, Lee AG.

Source

Department of Biochemistry, University of Southampton, U.K.

Abstract

Disulfiram [bis(diethylthiocarbamoyl)disulphide] has been found to stimulate reversibly the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum. At pH 7.2, 2.1 mM ATP and 25 degrees C, ATPase activity was found to double on addition of 120 microM disulfiram. Stimulation fitted to binding of disulfiram at a single site with a Kd of 61 microM. Disulfiram had no effect on the Ca2+ affinity of the ATPase or on the rate of phosphorylation of the ATPase by ATP, but increased the rate of dissociation of Ca2+ from the phosphorylated ATPase (the transport step) and increased the rate of dephosphorylation of the phosphorylated ATPase. It also decreased the level of phosphorylation of the ATPase by Pi, consistent with a 7.5-fold decrease in the equilibrium constant of the phosphorylated to non-phosphorylated forms (E2PMg/E2PiMg) at 80 microM disulfiram. Disulfiram had no significant effect on the concentration of ATP resulting in stimulation of ATPase activity, suggesting that it does not bind to the empty nucleotide-binding site on the phosphorylated ATPase. Studies of the effects of mixtures of disulfiram and jasmone (another molecule that stimulates the ATPase) suggest that they bind to separate sites on the ATPase.

3. Biochem J. 1995 May 15;308 ( Pt 1):343-6.

Evidence that the effects of phospholipids on the activity of the Ca(2+)-ATPase do not involve aggregation.

Starling AP, East JM, Lee AG.

Source

Department of Biochemistry, University of Southampton, U.K.

Abstract

The Ca(2+)-ATPase of skeletal-muscle sarcoplasmic reticulum, solubilized in monomeric from in C12E8, has been reconstituted by dialysis into sealed vesicles of dioleoyl phosphatidylcholine [di(C18:1)PC], dimyristoleoyl phosphatidylcholine [di(C14:1)PC], dinervonyl phosphatidylcholine [di(C24:1)PC] or dipalmitoyl phosphatidylcholine [di(C16:0)PC] in the gel phase, at a phospholipid/ATPase molar ratio of 10,000: 1. Cross-linking experiments show that ATPase molecules are present in these reconstituted vesicles as isolated monomeric species. ATPase activities for the reconstituted vesicles are about half of those for the ATPase reconstituted with the same lipid in unsealed membrane fragments, attributed to a close to random orientation for the ATPase molecules in the reconstituted vesicles. ATPase activities for the ATPase in reconstituted vesicles of di(C14:1)PC or di(C24:1)PC are less than in vesicles of di(C18:1)PC, and no activity could be detected for the ATPase in di(C16:0)PC in the gel phase. It is concluded that effects of lipids on the activity of the ATPase are independent of any changes in the state of aggregation of the ATPase. Inhibition of ATPase activity by spermine and by the hydrophilic domain of phospholamban are observed both for the unreconstituted ATPase and for the ATPase in reconstituted vesicles, so that inhibition is independent of any aggregation caused by these polycationic species. Stimulation of ATPase activity by jasmone is also observed both for the unreconstituted ATPase and for the ATPase in reconstituted vesicles, so that stimulation of the ATPase also does not follow from any change in the state of aggregation of the ATPase.

4. Biochemistry. 1994 Mar 15;33(10):3023-31.

Mechanism of stimulation of the calcium adenosinetriphosphatase by jasmone.

Starling AP, Hughes G, East JM, Lee AG.

Source

Department of Biochemistry, University of Southampton, U.K.

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.