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Showing papers on "Cooperativity published in 1987"


Journal ArticleDOI
TL;DR: Determination of the crystal structure of the trinuclear species has confirmed that it is indeed an inorganic double helix, possessing characteristic features (helical parameters, stacking of bipyridine bases) reminiscent of the DNAdouble helix.
Abstract: Two oligobipyridine ligands containing two and three 2,2'-bipyridine subunits separated by 2-oxapropylene bridges have been synthesized and some of their complexation properties with metal ions have been investigated. In particular, with copper(I) they form, respectively, a dinuclear and a trinuclear complex containing two ligand molecules and two or three Cu(I) ions. In view of the pseudotetrahedral coordination geometry of Cu(I) X bis(bipyridine) sites and of NMR data indicating that the present complexes are chiral, one may assign to these dinuclear and trinuclear species a double-helical structure in which two molecular strands are wrapped around two or three Cu(I) ions, which hold them together. These complexes may thus be termed "double-stranded helicates." Determination of the crystal structure of the trinuclear species has confirmed that it is indeed an inorganic double helix, possessing characteristic features (helical parameters, stacking of bipyridine bases) reminiscent of the DNA double helix. This spontaneous formation of an organized structure by oligobipyridine ligands and suitable metal ions opens ways to the design and study of self-assembling systems presenting cooperativity and regulation features. Various further developments may be envisaged along organic, inorganic, and biochemical lines.

681 citations


Journal Article
TL;DR: The Ca2+-ryanodine receptor complex is a functional unit at the terminal cisternae of the sarcoplasmic reticulum whose proteins comprise theCa2+ release channels which may be involved in excitation-contraction coupling.
Abstract: The Ca2+-ryanodine receptor complex is a functional unit at the terminal cisternae (TC) of the sarcoplasmic reticulum (SR) whose proteins comprise the Ca2+ release channels which may be involved in excitation-contraction coupling. Ca2+, Mg2+, caffeine, and adenine nucleotides, but not inositol 1,4,5-trisphosphate, may exert their inotropic effects on skeletal muscle SR by direct allosteric modulation of the [3H]ryanodine-binding site. Micromolar Ca2+ is primarily responsible for activating [3H]ryanodine binding by regulating receptor site density, affinity, and cooperativity. Mg2+ reduces the sensitivity to Ca2+ activation by directly competing with Ca2+ for the activator site. However, inhibition by Mg2+ is overcome in the presence of beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP; 1 mM) or caffeine (20 mM). Caffeine dramatically increases the affinity of the Ca2+ activator site for Ca2+, whereas AMP-PCP or cAMP enhances the gating efficiency or the lifetime of the open state of the TC SR channel. A kinetic model is proposed for four functional domains of the Ca2+-ryanodine receptor complex: the Ca2+-regulatory domain which binds Ca2+ with microM affinity is primarily responsible for gating the Ca2+ channel of the TC SR in a cooperative manner, and is inhibited by mM Mg2+ by direct competition for the activator site which appears to contain critical sulfhydryl groups; a Ca2+-activate alkaloid binding domain in close proximity to the channel which binds ryanodine with nM affinity and rapidly occludes upon complex formation; a domain which binds caffeine with low (greater than mM) affinity and directly influences the sensitivity of the Ca2+-regulatory site; and a domain which binds adenine nucleotides with intermediate affinity (less than mM), does not require phosphorylation, and intensifies the Ca2+ signal which triggers opening of the Ca2+-release channel.

311 citations


Journal ArticleDOI
01 Jan 1987
TL;DR: Hydration Water and Hydrogen Bonds: Experimental Difficulties, Cooperativity, and Three-Center Bonds and Cooperativity in Cyclic Mot!fs Formed by O-H Groups.
Abstract: PERSPECTIVES aND OVERVIEW 93 Hydration Water and Hydrogen Bonds: Experimental Difficulties, Cooperativity, and Three-Center Bonds 94 CYCLODEXTRIN HYDRATES AS MODEL SYSTEMS FOR THE STUDY OF HYDROGEN BONDING .. 96 Cooperativity in Cyclic Mot!fs Formed by O-H Groups 97 Cooperativity of Hydrogen Bonding Flip-Flop Dynamics 98

266 citations


Journal ArticleDOI
TL;DR: Investigation of the reaction of nitric oxide with ferric heme proteins and model compounds suggests that the presence of an axial water molecule at the ligand binding site of ferric hemoglobin A prevents it from exhibiting significant cooperativity in its reactions with NO.
Abstract: Rates for the reaction of nitric oxide with several ferric heme proteins and model compounds have been measured. The NO combination rates are markedly affected by the presence or absence of distal histidine. Elephant myoglobin in which the E7 distal histidine has been replaced by glutamine reacts with NO 500-1000 times faster than do the native hemoglobins or myoglobins. By contrast, there is not difference in the CO combination rate constants of sperm whale and elephant myoglobins. Studies on ferric model compounds for the R and T states of hemoglobin indicate that their NO combination rate constants are similar to those observed for the combination of CO with the corresponding ferro derivatives. The last observation suggests that the presence of an axial water molecule at the ligand binding site of ferric hemoglobin A prevents it from exhibiting significant cooperativity in its reactions with NO.

243 citations



Journal ArticleDOI
TL;DR: A model of the allosteric regulation of the dimeric flavoprotein methylenetetrahydrofolate reductase by the inhibitor, AdoMet, and by one of the substrates, NADPH, predicts the observed features of the equilibrium and kinetic data.

152 citations


Journal ArticleDOI
TL;DR: A sequential mechanism of calcium binding and translocation is proposed, that accounts for binding cooperativity and exchange kinetics, presteady state transients following addition of ATP, and the Ca2+ concentration dependence of ATPase activity in steady state.

141 citations


Journal ArticleDOI
TL;DR: Based on binding data, the UASrpg sequence ACACCCATACAT appears to be the one recognized most efficiently by the TUF factor, while competition experiments disclosed the existence of an additional binding component, distinct from TUF, that may possibly regulate a subset of genes for the translational apparatus.
Abstract: Transcription activation of yeast ribosomal protein genes is mediated through homologous, 12-nucleotide-long and, in general, duplicated upstream promoter elements (HOMOL1 and RPG, referred to as UASrpg). As shown previously, a yeast protein factor, TUF, interacts specifically with these conserved boxes in the 5'-flanking sequences of the elongation factor genes TEF1 and TEF2 and the ribosomal protein gene RP51A. We have now extended our studies of TUF-UASrpg binding by analysing--using footprinting and gel electrophoretic retardation techniques--the genes encoding the ribosomal proteins L25, rp28 (both copy genes), S24 + L46 and S33. Most, but not all, conserved sequence elements occurring in front of these genes, turned out to represent binding sites for the same factor, TUF. The two functionally important boxes that are found in a tandem arrangement (a characteristic of many rp genes) upstream of the L25 gene are indistinguishable in their factor binding specificity. Large differences were shown to exist in the affinity of the TUF factor for the various individual boxes and in the half-life of the protein-DNA complexes. No binding cooperativity could be demonstrated on adjacent sites on L25 or RP51A promoters. Based on binding data, the UASrpg sequence ACACCCATACAT appears to be the one recognized most efficiently by the TUF factor. Previously, no conserved box was found in front of the gene encoding S33. Nevertheless, complex formation with the protein fraction used was observed in the upstream region of the S33 gene. Competition experiments disclosed the existence of an additional binding component, distinct from TUF. This component may possibly regulate a subset of genes for the translational apparatus.

110 citations


Journal ArticleDOI
TL;DR: The experimental results are inconsistent with the one- site model but are explained by a two-site model in which the ternary complexes of So .

105 citations


Journal ArticleDOI
TL;DR: Purified enzyme is active as a monomeric species, exhibits high cooperativity between Ca+2 and phosphatidylserine binding for activity, and undergoes intramolecular self-phosphorylation at both serine and threonine residues.

100 citations


Journal ArticleDOI
TL;DR: The physiological role of Root effect haemoglobins is demonstrably not inevitably linked to the swim bladder but more probably arose from the need to oxygenate the poorly vascularized retina of many fishes.
Abstract: Considering the presently available data it is clear that the Root effect represents an exaggerated alkaline Bohr effect which occurs in the absence of a normal acid Bohr effect and is associated with a loss of oxygen binding capacity at low pH. Undoubtedly at the molecular level the presence of a Ser residue at position F9(94) beta in these haemoglobin is of primary importance. No Root effect haemoglobin has yet been identified which lacks this substitution. On the other hand however many haemoglobins are known which possess this Ser residue and at the same time lack a Root effect. Other factors arising from interactions at other sites in the haemoglobin molecule are obviously sufficient to negate the otherwise stabilizing effect of this critical Ser residue. The loss of cooperativity of Root effect systems as the pH is lowered is readily explained as due to stabilization of the low affinity T state to such a degree that the switch to the high affinity R state is suppressed even in the fully liganded molecule. The observation of Hill coefficients of less than unity requires that within the T state chain heterogeneity exists such that the alpha and beta chain haems demonstrate significantly different affinities for ligand. The physiological role of Root effect haemoglobins is demonstrably not inevitably linked to the swim bladder but more probably arose from the need to oxygenate the poorly vascularized retina of many fishes.(ABSTRACT TRUNCATED AT 250 WORDS)

Journal ArticleDOI
TL;DR: It is predicted here that the nucleotide-binding domain of alpha-subunit is formed by the amino acids in the sequence from residue 160 to approximately residue 340, which is suggested to be important for beta-alpha-beta intersubunit conformational interaction involved in positive catalytic cooperativity in F1-ATPase.

Journal ArticleDOI
TL;DR: The data presented demonstrate that the sulfate esters and a molecular weight in excess of approximately 15,000 are required for high affinity binding of the fucans to bindin, and suggest that the binding mechanism is not a simple ionic interaction and that hydrogen bonding and cooperativity may also be important determinants of the binding mechanisms.

Journal ArticleDOI
TL;DR: In this article, the allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb−O2 equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analyzed in terms of the MWC two state model and the Adair four step oxygenation theory.
Abstract: The allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb−O2 equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analysed in terms of the MWC two state model and the Adair four step oxygenation theory. At low concentrations (NTP/Hb ratio=1.0, and pH>7.3) ATP, GTP and protons decrease Hb−O2 affinity by increasing the allosteric constantL and reducingK T, the association constant1 of the deoxy, tense state of the Hb, without significantly affecting that (K R) of the oxy state, increasing the free energy of cooperativity (ΔG). High concentrations of these effectors, however, also reduceK R. The greater sensitivity of the half-saturation O2 tension (P 50) of the Hb to GTP than to ATP at the same concentration, correlates with greater effects of GTP on bothK T andK R. The pH and NTP dependence of the four Adair association constants and the calculated fractional populations of Hb molecules in different stages of oxygenation show that the autochthonous NTP effectors and protons stabilize the T structure and postpone the T→R transition basic to cooperativity in fish Hb. The possible implications of the findings for aquatic respiration are discussed.

Journal ArticleDOI
TL;DR: In this paper, a new definition for a cooperativity parameter is proposed, based on the two-body, non-neighbour interaction energy, plus three- and four-body contributions, including one-body deformation terms in relation to the total interaction energy of the water tetramer.
Abstract: The additional energy stabilization due to cooperative effects was calculated in extended hydrogen bonded systems OH OH OH with unidirectional (homodromic) orientation of the OH groups. Ab initio restricted Hartree Fock, MP2 and MP3 calculations with geometry optimization and BSSE correction have been performed using the GAUSSIAN 83 program package for the ground states of the linear water dimer with Cs symmetry and the cyclic water tetramer with S4 symmetry. The latter represents the smallest possible, experimentally observed cooperative structure. A new definition for a cooperativity parameter is proposed. The definition is based on the two-body, non-neighbour interaction energy, plus three- and four-body contributions, including one-body deformation terms in relation to the total interaction energy of the water tetramer. The advantage of this definition is its independence of the reference system, which is necessary in complicated molecular systems with an undefined number of hydrogen bonds, such as disordered or flip-flop systems. According to this definition the energy gain based on cooperativity in the S4 water tetramer is 29% with the MP3/6-31G** approximation, (30% with HF/4-31G* and 46% with HF/3-21G). The largest contribution of 18% is due to the three-body term on the MP3/6-31G** level, followed by the two-body, non-neighbour term with 11%. The four-body term and the deformation term are in the order of 1% and cancel each other because they have opposite sign.

Journal ArticleDOI
TL;DR: The observed effects on the cooperativity of the unfolding transition suggest that methanol and lower temperatures may increase the concentration of partially folded intermediate states in the unfolding of ribonuclease.
Abstract: The effect of methanol on the thermal denaturation of ribonuclease A has been investigated over the -40 to 70 degrees C range. The transition was fully reversible to at least 60% (v/v) methanol at an apparent pH of cryosolvent (pH) of 3.0 and was examined at methanol concentrations as high as 80%. The unfolding transition, as monitored by absorbance change at 286 nm, became progressively broader and occurred at increasingly lower temperatures as the alcohol concentration increased. In 50% methanol, increasing the pH from 2 to 6 shifted the transition to higher temperature. A substantial decrease in cooperativity was noted at the more acidic conditions. On the other hand, increasing concentrations of guanidine hydrochloride in 50% methanol caused the transition to shift to lower temperatures with little effect on the cooperativity. The observed effects on the cooperativity of the unfolding transition suggest that methanol and lower temperatures may increase the concentration of partially folded intermediate states in the unfolding of ribonuclease. Comparison of the transition in 50% methanol as determined by absorbance or fluorescence, which monitor the degree of exposure of buried tyrosines and hence the tertiary structure, to that determined by far-UV circular dichroism, which monitors secondary structure, indicated that the major unfolding transition occurred at a higher temperature in the latter case. Thus, the tertiary structure is lost at a lower temperature than the secondary structure. This observation is consistent with a model of protein folding in which initially formed regions of secondary structure pack together, predominantly by hydrophobic interactions, to give the tertiary structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Journal ArticleDOI
TL;DR: Recombinant human interleukin 1 beta has been studied in solution with respect to its conformation, stability, and characteristics of unfolding and refolding, finding an unusual biphasic change in fluorescence on unfolding.
Abstract: Recombinant human interleukin 1 beta has been studied in solution with respect to its conformation, stability, and characteristics of unfolding and refolding. It is an all-beta-type, stable globular protein with a high cooperativity under conditions where refolding is reversible. The tryptophan residue is approximately 40% exposed to solvent, and the four tyrosines are 50% exposed. The fluorescence of the single tryptophan residue is quenched at pH 7.5 but dequenched by high salt, by titration to lower pH with a pK of 6.59, and by denaturants, resulting in an unusual biphasic change in fluorescence on unfolding. Both histidine and thiol residues have been excluded as being responsible for the pH dependence of fluorescence by site-directed mutagenesis and by chemical modification, respectively. The likely candidate is an aspartate or glutamate.

Journal ArticleDOI
TL;DR: An allosteric model is presented that provides a simple explanation for the low population of triply ligated species, relative to the other species, in the oxygenation of human hemoglobin tetramers as found in high-concentration studies.
Abstract: An allosteric model is presented that provides a simple explanation for the low population of triply ligated species, relative to the other species, in the oxygenation of human hemoglobin tetramers as found in high-concentration studies [Gill, S J, Di Cera, E, Doyle, M L, Bishop, G A, & Robert, C H (1987) Biochemistry (preceding paper in this issue)] The model is a quantitative interpretation of the Perutz mechanism [Perutz, M F (1970) Nature (London) 228, 726-739] and is based on a number of structural and thermodynamic findings so far reported in the analysis of hemoglobin properties Human hemoglobin is assumed to exist in two quaternary states: the T or low-affinity state and the R or high-affinity state An extreme chain heterogeneity in the T state is postulated so that oxygen binds only to the alpha chains Nearest-neighbor interactions between the alpha chains may lead to cooperativity within the T state The R state is noncooperative, and both the alpha and beta chains have equal oxygen affinity

Journal ArticleDOI
TL;DR: Binding experiments by means of ultrafiltration proved that the red cell membrane actually binds to deoxyHb much more strongly than to oxyHb, validating the present conclusion based on oxygenation experiments.
Abstract: The mode of interaction of human hemoglobin (Hb) with the red cell membrane was investigated with special reference to the effect on oxygen binding properties and Hb-membrane binding constants. Compared to free native Hb, the membrane-bound native Hb showed a strikingly lowered oxygen affinity and smaller response to organic phosphates such as 2,3-diphosphoglycerate and inositol hexaphosphate. Similar effects of membrane binding were also observed for intermediately cooperative Hbs such as N-ethylmaleimide-treated Hb (NES-Hb) and iodoacetamide-treated Hb (AA-Hb), but very small effects were observed for non-cooperative Hb, i.e., carboxypeptidase A-treated Hb (des-His-Tyr Hb). The magnitude of the affinity lowering was in the order: NES-Hb greater than native Hb greater than AA-Hb much greater than des-His-Tyr Hb. In the presence of inositol hexaphosphate, the three chemically modified Hbs showed an increased oxygen affinity when bound to the red cell membrane, probably due to partial replacement of bound inositol hexaphosphate by membrane. The binding to membrane caused a slight decrease in cooperativity for native Hb, but no distinct change in cooperativity was observed for the three modified Hbs. These results imply: a) the red cell membrane binds to deoxyHb more strongly than to oxyHb; b) the difference in membrane binding affinity between oxyHb and deoxyHb is closely related to the quaternary structure change in the Hb molecule occurring upon oxygenation. The higher affinity of the membrane for deoxyHb than for oxyHb apparently disagrees with the conclusion drawn by earlier investigators. However, the present binding experiments by means of ultrafiltration proved that the red cell membrane actually binds to deoxyHb much more strongly than to oxyHb, validating the present conclusion based on oxygenation experiments. Our results are consistent with those obtained recently by other investigators using a synthetic peptide or the cytoplasmic fragment of red cell membrane band 3.

Journal ArticleDOI
TL;DR: A model in which troponin/tropomyosin (Tn/Tm) controls the actin-S1 interaction by inhibiting the isomerization step is proposed and can account for the cooperative binding of S1 and S1 nucleotide complexes to actin.

Journal ArticleDOI
TL;DR: Results confirm that R subunit sequences implicated in cAMP binding by homology with other cyclic nucleotide-binding proteins actually correspond to functional cAMP-binding sites.

Journal ArticleDOI
TL;DR: The first direct equilibrium dialysis titration of the blood coagulation protein bovine prothrombin fragment 1 with Mg(II) is presented and a model for the binding of Ca(II).

Journal ArticleDOI
TL;DR: The interactions of the PCDF radioligands with the cytosolic receptor all exhibited saturable binding curves and linear Scatchard plots and the slopes of their Hill plots were in the range 1.0-1.1, thus indicating that cooperativity was not a factor in these binding interactions, and there may be a temporal shift in ligand binding affinities.

Journal ArticleDOI
TL;DR: The model predicts that Ca2+ binding should be a mandatory requirement for phosphorylation of the pump protein, though ATP binding per se does not require Ca2+.
Abstract: The conventional alternating access model for Ca2+ transport by the sarcoplasmic reticulum Ca2+ pump is modified, partly on the basis of the proposed MacLennan-Green domain structure for the Ca2+-pump protein. The present model divides the uptake state (E1) of the protein into three substates, differing in the condition of the Ca2+-binding domain. The domain is an open cavity in the first substate and can bind only a single Ca2+ ion. A fast "jaw-closing" (or "hinge-bending") step then partially closes the cavity to generate the second substate that has a second Ca2+-binding site. Occupation of this site is followed by another jaw-closing step that closes the binding cavity and occludes the bound ions. The subsequent translocation step (to form E2) remains unchanged from previous models. The modified model predicts a constant transport stoichiometry of two Ca2+ per pump reaction cycle. It suggests a plausible mechanism for coupling between Ca2+ binding and ATP utilization: the model predicts (in agreement with experiment) that Ca2+ binding should be a mandatory requirement for phosphorylation of the pump protein, though ATP binding per se does not require Ca2+. The model is consistent with high cooperativity in equilibrium binding of Ca2+, both in the absence and presence of ATP.

Journal ArticleDOI
TL;DR: Dynamic Monte Carlo studies on diamond lattice models of β‐proteins strongly suggest that the uniqueness of the globular conformation requires some residual secondary structure to be present in the denatured state.
Abstract: Dynamic Monte Carlo studies have been performed on various diamond lattice models of β-proteins. Unlike previous work, no bias toward the native state is introduced; instead, the protein is allowed to freely hunt through all of phase space to find the equilibrium conformation. Thus, these systems may aid in the elucidation of the rules governing protein folding from a given primary sequence; in particular, the interplay of short- vs long-range interaction can be explored. Three distinct models (AC) were examined. In model A, in addition to the preference for trans (t) over gauche states (g+ and g−) (thereby perhaps favoring β-sheet formation), attractive interactions are allowed between all nonbonded, nearest neighbor pairs of segments. If the molecules possess a relatively large fraction of t states in the denatured form, on cooling spontaneous collapse to a well-defined β-barrel is observed. Unfortunately, in model A the denatured state exhibits too much secondary structure to correctly model the globular protein collapse transition. Thus in models B and C, the local stiffness is reduced. In model B, in the absence of long-range interactions, t and g states are equally weighted, and cooperativity is introduced by favoring formation of adjacent pairs of nonbonded (but not necessarily parallel) t states. While the denatured state of these systems behaves like a random coil, their native globular structure is poorly defined. Model C retains the cooperativity of model B but allows for a slight preference of t over g states in the short-range interactions. Here, the denatured state is indistinguishable from a random coil, and the globular state is a well-defined β-barrel. Over a range of chain lengths, the collapse is well represented by an all-or-none model. Hence, model C possesses the essential qualitative features observed in real globular proteins. These studies strongly suggest that the uniqueness of the globular conformation requires some residual secondary structure to be present in the denatured state.

Journal ArticleDOI
TL;DR: It is concluded that plasma membrane of canine intestinal circular muscle contains neurotensin receptors with recognition properties distinct from those obtained in previous studies of neurotens in binding sites in murine tissues.

Journal ArticleDOI
TL;DR: The results are not consistent with the alternative model, which predicts that if pPDM X S-1.ATP binds to actin in the absence of Ca2+ but does not turn on the ATPase activity, then it should also not turnOn the ATP enzyme activity in the presence ofCa2+.
Abstract: In our model of regulation, the observed lack of cooperativity in the binding of myosin subfragment 1 (S-1) with bound ATP to the troponin-tropomyosin-actin complex (regulated actin) is explained by S-1.ATP having about the same affinity for the conformation of the regulated actin that activates the myosin ATPase activity (turned-on form) and the conformation that does not activate the myosin ATPase activity (turned-off form). This predicts that, in the absence of Ca2+, S-1.ATP should not turn on the regulated actin filament. In the present study, we tested this prediction by using either unmodified S-1 or S-1 chemically modified with N,N'-p-phenylenedimaleimide (pPDM X S-1) so that functionally it acts like S-1.ATP, although it does not hydrolyze ATP. We found that, in the absence of Ca2+, neither S-1.ATP nor pPDM X S-1.ATP significantly turns on the ATPase activity of the regulated complex of actin and S-1 (acto X S-1). In contrast, in the presence of Ca2+, pPDM X S-1.ATP binding almost completely turns on the regulated acto.S-1 ATPase activity. These results can be explained by our original cooperativity model, with pPDM X S-1.ATP binding only approximately equal to 2-fold more strongly to the turned-on form than to the turned-off form of regulated actin. However, our results are not consistent with our alternative model, which predicts that if pPDM X S-1.ATP binds to actin in the absence of Ca2+ but does not turn on the ATPase activity, then it should also not turn on the ATPase activity in the presence of Ca2+.

Journal ArticleDOI
TL;DR: The results indicate that hemoglobin concentration in the 0.1-0.02 mM range does not significantly affect the kinetic rates, and the alpha chains dissociate CO faster than the beta chains; the symmetrical diliganded intermediates show cooperativity with respect to ligand dissociation that disappears in the presence of inositol hexaphosphate.

Journal ArticleDOI
TL;DR: It is suggested that Asp-59 in oncomodulin binds metal only indirectly through an intervening water molecule, a proposal which is consistent with the CD site's reduced affinity for ions the size of Ca(II) or smaller.

Journal ArticleDOI
TL;DR: Insight is provided into the role of bound ions in modifying lateral phase behavior in phospholipid membranes and great potential for infrared spectroscopy is demonstrated as a means to relate these Tb3+ luminescence studies to experiments involving less tractable cations.