Re-Examination of the Apparent Binding Constant of Ethylene Glycol Bis(β-Aminoethyl Ether)-N,N,N',N'-Tetraacetic Acid with Calcium around Neutral pH12

Harafuji, Hikaru; Ogawa, Yasuo

doi:10.1093/oxfordjournals.jbchem.a132868

Cited by 395 publications

(141 citation statements)

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“…All other reagents were of analytical grade. Free Ca 2+ was calculated using values of 8.79x 105 M 1 and 1.82x 10 ~ M -~ as the apparent binding constants for Ca z+ of EGTA [14] and of AMPOPCP [15], respectively, regardless of salt concentrations. Under the conditions used, [3-RyR showed higher sensitivity for Ca 2+ than c~-RyR as reported previously [11].…”

Section: Methodsmentioning

confidence: 99%

Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Murayama

Ogawa

1996

FEBS Letters

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Section: Methodsmentioning

confidence: 99%

Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Murayama

Ogawa

1996

FEBS Letters

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“…This value lies near the upper end of the range of values that have been measured in vitro with 100 mM KC1. Harafuji and Ogawa (1980) obtained values of 1.0-3.0 X 106 M-is -x at 20~ and Smith et al (1984) obtained a value of 0.9 • 106 M-is -1 at 16~ Harafuji and Ogawa (1980) attributed the differences among their values to the three different pH buffers that were used. Our estimate of kl would be smaller than 2.5 • 106 M-is -1 if the value of [EGTA]R were greater than 18.24 mM; for example, the concentration of free EGTA might be essentially the same as that in the end pools, as seems likely after the long periods of equilibration that were used in our experiments, and an additional amount of EGTA might be bound inside the myoplasm and able to react with Ca.…”

Section: (Ms) 500mentioning

confidence: 99%

“…First, in the stopped-flow experiments of Smith et al (1984), the rate of Ca complexation by EGTA was determined from measurements of changes in pH whereas, in another series of stopped-flow experiments (Harafuji and Ogawa, 1980), it was determined from measurements of changes in free [Ca]. The values of kl that were obtained by Harafuji and Ogawa (1980), 1.0-3.0 • 106 M-is -1 at 20~ are in good agreement with the value obtained by Smith et al (1984), 1.5 • 106 M-as -x at 25~ consistent with the idea that there is little delay between the complexation of Ca by H2EGTA 2-and the dissociation of protons from CaH2EGTA. Second, in the experiments of Smith et al (1984), the change in pH began almost immediately after mixing and showed no detectable delay, also suggesting that protons dissociate from CaH2EGTA almost immediately after Ca is complexed by H~EGTA 2-.…”

Section: At Neutral Ph Ca Z+ Is Complexed By H2egtae-and Two Protonsmentioning

confidence: 99%

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Pape

Jong

Chandler

1995

The Journal of General Physiology

129

295

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Sarcoplasmic reticulum (SR) Ca release was studied at 13-16~ in cut fibers (sarcomere length, 3.4-3.9 I~m) mounted in a double Vaseline-gap chamber. The amplitude and duration of the action-potential stimulated free [Ca] transient were reduced by equilibration with end-pool solutions that contained 20 mM EGTA with 1.76 mM Ca and 0.63 mM phenol red, a maneuver that appeared to markedly reduce the amount of Ca complexed by troponin. A theoretical analysis shows that, under these conditions, the increase in myoplasmic free [Ca] is expected to be restricted to within a few hundred nanometers of the SR Ca release sites and to have a time course that essentially matches that of release. Furthermore, almost all of the Ca that is released from the SR is expected to be rapidly bound by EGTA and exchanged for protons with a 1:2 stoichiometry. Consequently, the time course of SR Ca release can be estimated by scaling the ApH signal measured with phenol red by -13/2. The value of 13, the buffering power of myoplasm, was determined in fibers equilibrated with a combination of EGTA, phenol red, and fura-2; its mean value was 22 mM/pH unit. The Ca content of the SR (expressed as myoplasmic concentration) was estimated from the total amount of Ca released by either a train of action potentials or a depleting voltage step; its mean value was 2,685 I~M in the action-potential experiments and 2,544 IxM in the voltage-clamp experiments. An action potential released, on average, 0.14 of the SR Ca content with a peak rate of release of,'~5 %/ms. A second action potential, elicited 20 ms later, released only 0.6 times as much Ca (expressed as a fraction of the SR content), probably because Ca inactivation of Ca release was produced by the first action potential. During a depolarizing voltage step to 60 mV, the rate of Ca release rapidly increased to a peak value of~3 %/ms and then decreased to a quasi-steady level that was only 0.6 times as large; this decrease was also probably due to Ca inactivation of Ca release. SR Ca release was studied with small step depolarizations that open no more than one SR Ca channel in 7

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“…Methods," but in the presence of 5 AM A23187, in the presence of the specified concentrations of Triton X-100 (A), lysolecithin (01), or Brij 58 (0), with 100 Mg membrane protein mL-1 (A (15,24,28). As detailed in "Materials and Methods," we have experimentally determined the value of the Ka of the Ca-EGTA complex in our assay conditions, which is about 10-fold lower than reported by ref.…”

Section: Dependence On Ca2+ Concentrationmentioning

confidence: 99%

Plasma Membrane Ca-ATPase of Radish Seedlings

Carnelli¹,

Michelis²,

Rasi‐Caldogno³

1992

Plant Physiol.

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In this work, we exploited the capability of the plasma membrane Ca-ATPase to utilize ITP as a substrate to study its characteristics in plasma membrane vesicles purified from radish (Raphanus sativus L.) seedlings. The Demonstrating the hydrolytic activity of the PM Ca-ATPase in native PM vesicles has proven difficult, due to the simultaneous operation of the much more active PM H+-ATPase, which is inhibited by Ca2", already in the micromolar range (5). Taking advantage of the different pH optima of the PM H+-ATPase (approximately 6.5) and of the PM CaATPase (7.0-7.5), we have shown that a Ca2e-dependent ATPase activity inhibited by submicromolar EB is localized at the PM ofradish seeds (21). The biochemical characteristics ofthis activity so far investigated, as well as its functional mol wt determined by radiation-inactivation, are very similar to those determined for ATP-dependent Ca2`uptake into PM vesicles, indicating that it represents the hydrolytic activity of the PM Ca-ATPase (21-23). However, the simultaneous operation of the Ca2t-inhibited PM H+-ATPase is an important source of error in these measurements because any treatment can be expected to influence both activities in the same or in the opposite sense. Because the PM H+-ATPase is highly specific for ATP as a substrate (5), it should be possible to use ITP or GTP as a substrate to measure the hydrolytic activity of the PM Ca-ATPase in native PM vesicles, minimizing complications arising from the simultaneous operation of the H+-ATPase. Analysis of GTP-dependent Ca2" uptake into PM vesicles from red beet has shown that GTP is a useful means to probe the transport function of the PM Ca-ATPase (27), but no data are available on its suitability to measure the hydrolytic activity of this enzyme. Because the presence of regulatory GTP-binding

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Re-Examination of the Apparent Binding Constant of Ethylene Glycol Bis(β-Aminoethyl Ether)-N,N,N',N'-Tetraacetic Acid with Calcium around Neutral pH12

Cited by 395 publications

References 0 publications

Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Plasma Membrane Ca-ATPase of Radish Seedlings

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Re-Examination of the Apparent Binding Constant of Ethylene Glycol Bis(β-Aminoethyl Ether)-N,N,N',N'-Tetraacetic Acid with Calcium around Neutral pH12

Cited by 395 publications

References 0 publications

Similar Ca2+ dependences of [3H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Similar Ca2+ dependences of [3H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Plasma Membrane Ca-ATPase of Radish Seedlings

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Product

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Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium

Similar Ca²⁺ dependences of [³H]ryanodine binding to α‐ and β‐ryanodine receptors purified from bullfrog skeletal muscle in an isotonic medium