A Ca
 ++
 -Dependent and -Selective Ionophore as Part of the Ca
 ++
 + Mg
 ++
 -Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum

Shamoo, Adil E.; MacLennan, David H.

doi:10.1073/pnas.71.9.3522

Cited by 80 publications

(44 citation statements)

References 16 publications

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“…The purified ATPase is enzymatically inactivated by 50 /.~M Cd (MacLennan, 1970). Furthermore, when the purified solubilized ATPase functions as an ionophore in lipid membranes, Cd transport is negligible (A. E. Shamoo, personal communication), similar to published data for Zn (Shamoo and MacLennan, 1974).…”

Section: Mg Dependence Of Ca Uptake In Skinned Fiberssupporting

confidence: 66%

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Stephenson¹,

Podolsky²

1977

The Journal of General Physiology

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A B S T R A C T The effect of Mg on Ca movement between the sarcoplasmic reticulum (SR) and myofilament space (MFS) was studied in skinned muscle fibers by using isometric force as an indicator of MFS Ca. In Ca-loaded fibers at 20°C, the large force spike induced by Ca in 1 mM Mg (5 mM ATP) was strongly inhibited in 3 mM Mg, and force development was extremely slow. After a brief Ca stimulus in 1 mM Mg, relaxation in Ca-free solution was significantly faster in 3 mM Mg. These changes were due to altered Ca movements, since the effect of 3 mM Mg on steady force in CaEGTA solutions was small. Changes in Mg alone induced force transients apparently due to altered Ca movement. In relaxed fibers, decreasing the Mg to 0.25 mM caused phasic force development. In contracting fibers in Ca solutions, increasing the Mg caused a large transient relaxation. The effects of increased Mg were antagonized by 0.5 mM Cd, an inhibitor of the SR Ca transport system. The results indicate that active Ca uptake by the SR in situ is stimulated by Mg, and that it can affect local MFS [Ca ++] in the presence of a substantial Ca source. These results provide evidence that an increased rate of Ca uptake in 3 mM Mg could account for inhibition of the large force spike associated with Ca-induced Ca release in skinned fibers. I N T R O D U C T I O NIn skinned fibers from skeletal muscle, calcium ions can cause a transient force spike (Ford and Podolsky, 1970;Endo et al., 1970) due to Ca release f r o m the sarcoplasmic reticulum (SR) to the myofilament space (MFS) (Ford and Podolsky, 1972 b). This regenerative effect reflects a Ca-sensitive efflux mechanism in the SR m e m b r a n e which could be an important feature o f excitation-contraction coupling in intact fibers. Excitation o f the transverse tubules could be transmitted to the SR by a small Ca signal (Ford and Podolsky, 1972 b), or a small a m o u n t o f Ca released f r o m the SR by some other signal could be required for the large increase in Ca efflux associated with contraction. Ca-induced force spikes were studied at low Mg ion concentration (<10 -4 M), and millimolar Mg ion prevented a large response (Ford and Podolsky, 1970). T h e mechanism underlying this inhibition is i m p o r t a n t both in assessing the role o f Ca-induced release in intact fibers, where free Mg is likely to be at least 10 -4 M, and in u n d e r s t a n d i n g the regulation o f net Ca m o v e m e n t between the intracellular compartments.Mg inhibition o f force spikes in skinned fibers could be related to an increased

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Section: Mg Dependence Of Ca Uptake In Skinned Fiberssupporting

confidence: 66%

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Stephenson¹,

Podolsky²

1977

The Journal of General Physiology

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“…As shown in Fig. 2, the maximum effect is achieved with a final concentration of less than 10 ,g of subunit 9 added per ml. It may be assumed that only added protein taken up by the planar membrane was effective, because rinsing the compartment after the effect is complete does not modify the results.…”

Section: Resultsmentioning

confidence: 89%

“…Workers in several laboratories in recent years have attempted to identify protein fractions in mitochondria that exhibit proton ionophore activity (3)(4)(5)(6)(7)(8)(9)(10). Racker has shown that mitochondrial and chloroplast proteolipids may act as ionophores in collapsing proton gradients generated by bacteriorhodopsin (4), but it was not shown that these proteolipids were in fact associated with ATPase nor was any specific relation between ionophoric activity and biological function of this protein demonstrated.…”

Section: Discussionmentioning

confidence: 99%

“…Although proton translocation is thought to proceed through the membrane sector of the complex, the components involved in the proton translocating mechanism remain unidentified. The concept that endogenous protein ionophores or protein-bound ionophores in the mitochondrial inner membrane may play an important role in energized membrane processes has recently been advanced by Green (2) and has been examined experimentally in several laboratories (3)(4)(5)(6)(7)(8)(9)(10).…”

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confidence: 99%

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Oligomycin-dependent ionophoric protein subunit of mitochondrial adenosinetriphosphatase.

Criddle¹,

Packer²,

Shieh³

1977

Proc. Natl. Acad. Sci. U.S.A.

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A proteolipid isolated from yeast mitochondrial adenosinetriphospitatase (subunit 9) (ATP phosphohydrolase; EC 3.6.1.3) by chloroform/methanol extraction has been shown to discharge photo-induced potentials across a planar phospholipid membrane containing bacteriorhodopsin. Oligomycin, a specific inhibitor of oxidative phosphorylation which binds to tis protein, allows the potential gradient to be reestablished. When proteolipid was isolated from an oligomycin-resistant strain, ionophoric activity was still obtained but the effect was not reversed by oligom cin. These studies suggest that the hydrophobic subunit-9 polypeptide is the ionopboric component linking ATP synthesis (hydrolysis) with proton translocation.Recent studies of mitochondrial oxidative phosphorylation have demonstrated a link between ATP hydrolysis or synthesis and the transmembrane movement of H+ (for review see ref.

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“…All of these studies deal with the effect of anionic detergents in the presence of monovalent cations. The effects of detergents on the conductivity and selectivity of membranes to divalent cations have not previously been dealt with, Our laboratory has a special interest in the effect of detergents on divalent cation conductance in black lipid membranes, since these detergents were used in the purification of proteins that possess ionophoric activity (Shamoo & MacLennan, 1974;Shamoo et al, 1976;Stewart et al, 1976 ;Abramson & Shamoo, 1978 ;Jeng, Ryan & Shamoo, 1978;Shamoo, 1978).…”

mentioning

confidence: 98%

Anionic detergents as divalent cation ionophores across black lipid membranes

Abramson

Shamoo

1979

J. Membrain Biol.

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Three ionic detergents commonly used in membrane-bound protein isolation and reconstitution experiments, SDS, cholate, and DOC, are shown to act as divalent cation ionophores when incorporated into black lipid membranes made from either oxidized cholesterol or a mixture of phosphatidylcholine and cholesterol (PC/cholesterol = 5:1 mg). At a concentration greater than or equal to 1 microM, SDS shows large selectivity differences between cations and anions and among the different cations tested (Ba2+, Ca2+, Sr2+, Mg2+, and Mn2+). Deoxycholate and cholate at concentrations greater than 4 X 10(-4) M and 10(-3) M, respectively, also act as divalent cation ionophores. The selectivity sequence measured for these two detergents is evidence for a strong ionic interaction between the divalent cation and the anionic charged groups on the detergent. In the case of cholate, the conductance depends on the third or fourth power of the cholate concentration and shows a linear dependence on CaCl2 concentration. The conductance for deoxycholate depends onthe sixth or seventh power of the DOC concentration and is also linearly dependent on the CaCl2 concentration. In an oxidized cholesterol black lipid membrane in the presence of 5 mM CaCl2, small concentrations of LaCl3 (less then 1 microM) inhibit the ionophoric activity of each of the detergents tested. Evidence is presented to show that this inhibitory effect is a nonspecific effect on oxidized cholesterol BLM's, and is not due to a direct effect of La3+ on detergent-mediated transport.

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A Ca ⁺⁺ -Dependent and -Selective Ionophore as Part of the Ca ⁺⁺ + Mg ⁺⁺ -Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum

Cited by 80 publications

References 16 publications

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Oligomycin-dependent ionophoric protein subunit of mitochondrial adenosinetriphosphatase.

Anionic detergents as divalent cation ionophores across black lipid membranes

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A Ca ++ -Dependent and -Selective Ionophore as Part of the Ca ++ + Mg ++ -Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum

Cited by 80 publications

References 16 publications

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.

Oligomycin-dependent ionophoric protein subunit of mitochondrial adenosinetriphosphatase.

Anionic detergents as divalent cation ionophores across black lipid membranes

Contact Info

Product

Resources

About

A Ca ⁺⁺ -Dependent and -Selective Ionophore as Part of the Ca ⁺⁺ + Mg ⁺⁺ -Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum