TY - JOUR
T1 - Effects of Vanadate on the Rotational Dynamics of Spin-Labeled Calcium Adenosinetriphosphatase in Sarcoplasmic Reticulum Membranes
AU - Lewis, Scott M.
AU - Thomas, David D
PY - 1986/8
Y1 - 1986/8
N2 - We have studied the effects of vanadate on the rotational motion of the calcium adenosine-triphosphatase (Ca-ATPase) from sarcoplasmic reticulum (SR), using saturation-transfer electron paramagnetic resonance (ST-EPR). Vanadate has been proposed to act as a phosphate analogue and produce a stable intermediate state similar to the phosphoenzyme. This study provides evidence about the physical state of this intermediate. In particular, since ST-EPR provides a sensitive measure of microsecond protein rotational mobility, and hence of protein-protein association, these studies allowed us to ask (a) whether the vanadate-induced protein association observed in electron micrographs of SR vesicles also occurs under physiological (as opposed to fixed, stained, or frozen) conditions and (b) whether vanadate-induced changes in protein association also occur under conditions sufficient for enzyme inhibition but not for the production of large arrays detectable by electron microscopy (EM). At 5 mM decavanadate, a concentration sufficient to crystallize the ATPase on greater than 90% of the membrane surface area in EM, ST-EPR showed substantial immobilization of the spin-labeled protein, indicating protein-protein association in the unstained vesicles. Conventional EPR spectra of lipid probes showed that lipid hydrocarbon chain mobility is unaffected by decavanadate-induced protein crystallization in SR, suggesting that changes in protein-protein contacts do not involve the lipid hydrocarbon region. At 5 mM monovanadate, a concentration sufficient to inhibit the ATPase but not to form crystals detectable by EM, no changes were observed in ST-EPR or conventional EPR spectra of either protein or lipid. In summary, these results indicate that decavanadate induces extensive self-association of the Ca-ATPase but that monovanadate inhibits without a change in protein mobility, thus indicating no change in oligomeric state. If monovanadate produces an analogue of a phosphoenzyme state that is important in the Ca-ATPase cycle, this phosphoenzyme has the same oligomeric state as the unphosphorylated enzyme. Alternatively, if decavanadate produces a phosphoenzyme analogue, the present results suggest that protein association is increased in the phosphoenzyme state.
AB - We have studied the effects of vanadate on the rotational motion of the calcium adenosine-triphosphatase (Ca-ATPase) from sarcoplasmic reticulum (SR), using saturation-transfer electron paramagnetic resonance (ST-EPR). Vanadate has been proposed to act as a phosphate analogue and produce a stable intermediate state similar to the phosphoenzyme. This study provides evidence about the physical state of this intermediate. In particular, since ST-EPR provides a sensitive measure of microsecond protein rotational mobility, and hence of protein-protein association, these studies allowed us to ask (a) whether the vanadate-induced protein association observed in electron micrographs of SR vesicles also occurs under physiological (as opposed to fixed, stained, or frozen) conditions and (b) whether vanadate-induced changes in protein association also occur under conditions sufficient for enzyme inhibition but not for the production of large arrays detectable by electron microscopy (EM). At 5 mM decavanadate, a concentration sufficient to crystallize the ATPase on greater than 90% of the membrane surface area in EM, ST-EPR showed substantial immobilization of the spin-labeled protein, indicating protein-protein association in the unstained vesicles. Conventional EPR spectra of lipid probes showed that lipid hydrocarbon chain mobility is unaffected by decavanadate-induced protein crystallization in SR, suggesting that changes in protein-protein contacts do not involve the lipid hydrocarbon region. At 5 mM monovanadate, a concentration sufficient to inhibit the ATPase but not to form crystals detectable by EM, no changes were observed in ST-EPR or conventional EPR spectra of either protein or lipid. In summary, these results indicate that decavanadate induces extensive self-association of the Ca-ATPase but that monovanadate inhibits without a change in protein mobility, thus indicating no change in oligomeric state. If monovanadate produces an analogue of a phosphoenzyme state that is important in the Ca-ATPase cycle, this phosphoenzyme has the same oligomeric state as the unphosphorylated enzyme. Alternatively, if decavanadate produces a phosphoenzyme analogue, the present results suggest that protein association is increased in the phosphoenzyme state.
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U2 - 10.1021/bi00364a024
DO - 10.1021/bi00364a024
M3 - Article
C2 - 3021193
AN - SCOPUS:0022544929
VL - 25
SP - 4615
EP - 4621
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 16
ER -