Structure-activity relationship of channel binding affinity of quaternary ammonium ions

目的：探讨季铵离子在钾通道外部结合位点的结构活性关系．方法：用ＩｎｓｉｇｈｔＩＩ分子建模软件包和ＭＯＰＡＣ６０计算每个季铵离子的水化自由能（ΔＧｈｙｄｒａｔｉｏｎ）、最高占有轨道能量（ＥＨＯＭＯ）和最低未占有轨道能量（ＥＬＵＭＯ）．结合自由能与这些描述参数之间的关系用偏最小二乘法进行回归．结论：一般说来，季铵离子ＥＬＵＭＯ越高，溶剂化就越弱，相应的亲和力就越强．对于比四乙铵大（ＴＥＡ）的季铵离子，其大的分子尺寸不利于它对通道的亲和力．结论：所有季铵离子的通道亲和力与ΔＧｈｙｄｒａｔｉｏｎ和ＥＬＵＭＯ有很好的相关性．     

Drug binding in the undernourished: a study of the binding of propranolol to α 1-acid glycoprotein

Summary The binding of propranolol, a drug commonly used in cardiovascular disorders, to ₁-acid glycoprotein (AGP) was studied in vitro in malnutrition. Compared to normal and hospital controls, the level of AGP was found to be elevated in undernourished subjects with and without infection. In the same patients the free drug percentage was significantly diminished. A significant inverse relationship was observed between the percentage of free drug and the level of AGP. The finding suggests that there may be need for an altered dosage regimen in the undernourished.     

Characterization of α(2B)-adrenoceptor ligand binding in the presence of muscarinic toxin α and delineation of structural features of receptor binding selectivity

Nicotinic acetylcholine receptors mediate fast cholinergic modulation of glutamatergic transmission and synaptic plasticity. Here we investigated the effects of subtype selective activation of the α7 nicotinic acetylcholine receptors on hippocampal transmission and the inhibition of synaptic long-term potentiation by the Alzheimer's disease associated amyloid ?-protein (A?). The α7 nicotinic acetylcholine receptor agonist "compound A" ((R)-N-(1-azabicyclo[2.2.2]oct-3-yl)(5-(2-pyridyl))thiophene-2-carboxamide) induced a rapid-onset persistent enhancement of synaptic transmission in the dentate gyrus in vitro. Consistent with a requirement for activation of α7 nicotinic acetylcholine receptors, the type II α7-selective positive allosteric modulator PheTQS ((3aR, 4S, 9bS)-4-(4-methylphenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide) potentiated, and the antagonist methyllycaconitine (MLA) prevented the persistent enhancement. Systemic injection of the agonist also induced a similar MLA-sensitive persistent enhancement of synaptic transmission in the CA1 area in vivo. Remarkably, although compound A did not affect control long-term potentiation (LTP) in vitro, it prevented the inhibition of LTP by A?1-42 and this effect was inhibited by MLA. These findings strongly indicate that activation of α7 nicotinic acetylcholine receptors is sufficient to persistently enhance hippocampal synaptic transmission and to overcome the inhibition of LTP by A?.     

Bivalent sequential binding of docetaxel to methyl-β-cyclodextrin

New docetaxel (Dtx) and cyclodextrin (CD) inclusion complexes having improved apparent water solubility (up to 9.98 mg mL⁻¹) were obtained from phase solubility diagrams. γ-CD and SBE-β-CD offered only poor solubility enhancements while considerable increases in apparent solubility were obtained with Me-β-CD (20%, w/w) and HP-β-CD (40%, w/w) (9.98 mg mL⁻¹ and 7.43 mg mL⁻¹, respectively). The complexation mechanism between Dtx and Me-β-CD was investigated by circular dichroism spectrometry, two-dimensional ¹H NMR (NOESY) in D₂O, isothermal titration calorimetry (ITC) and molecular docking calculations. Circular dichroism and NOESY confirmed the existence of non-covalent interactions between Dtx and Me-β-CD and suggested that the tert-butyl group (C₆-C₉) and two aromatic groups (C₂₄-C₂₉ and C₃₀-C₃₅) of Dtx interacted with the Me-β-CD molecules. The combination of ITC results to molecular docking calculations led to the identification of an unconventional sequential binding mechanism between Me-β-CD and Dtx. In this sequential binding, a Me-β-CD molecule first interacted with both tert-butyl and C₃₀-C₃₅ aromatic groups (K₁: 744 M⁻¹). Then a second Me-β-CD molecule interacted with the C₂₄-C₂₉ aromatic group (K₂: 202 M⁻¹). The entropy of the first interaction was positive, whereas a negative value of entropy was found for the second interaction. The opposite behavior observed for these two sites was explained by differences in the hydrophobic contact surface and functional group flexibility.     

Properties of agonist binding at theβ-adrenoceptor of the rat reticulocyte

Summary To study the fundamental differences between agonist and antagonist interaction with the -adrenoceptor of the rat reticulocyte the radiolabeled agonist³H hydroxybenzylisoprenaline (³H HBI) and the radiolabeled antagonist³H dihydroalprenolol (³H DHA) were used.Equilibrium binding experiments with³H HBI revealed all characteristics expected to a -adrenoceptor site, i. e. high affinity binding (K _{D high}=7.4±0.9×10^–9 M), saturability (B _{max high}=230±24 fmoles/mg protein), and stereoselectivity. The rank order of potency for competing agonists was isoprenaline > adrenaline > noradrenaline > dopamine.³H HBI high affinity binding sites amounted to about 25% of -adrenoceptor sites detectable with³H DHA.In competition experiments with³H HBI and (-)isoprenaline[(-)Ipn]aK _{D high}-value for (-)Ipn of 3.1±0.6×10^–8M was obtained corresponding to theK _{D high}-value of (-)Ipn obtained from competition experiments using³H DHA. For (-)propranololK _D-values of 0.9±0.5×10^–8 M and 1.0 ±1.0×10^–8 M were measured using³H HBI and³H DHA respectively.Agonist affinity derived from competition experiments with (-)Ipn versus³H DHA was not affected by temperature changes.Guanylyl-imidodiphosphate [Gpp(NH)p] decreased concentration dependently the number of high affinity binding sites of³H HBI not affecting the respectiveK _D-value. Similar effects were observed after omission of Mg²⁺ from the binding assay or inclusion of Na⁺ in the Mg²⁺-free incubation mixture.The association reaction of³H HBI at the -adrenoceptor revealed two different velocities. The slower phase of the association reaction which represents high affinity binding (80% of equilibrium binding) is not observed in the presence of Gpp(NH)p.A biphasic dissociation of³H HBI binding was induced by 10^–4 M (±)propranolol: 25% dissociated with at _1/2 of 1.3 min whereas the high affinity binding was reversed with at _1/2 of 150 min. This slowly reversible binding of³H HBI however was rapidly reversed by Gpp(NH)p (t _1/2<1 min).It is concluded that the agonist ligand³H HBI permits a direct qualitative and quantitative characterization of the agonist induced high affinity state of the -adrenoceptor. In particular, the kinetic studies strongly support a two step binding model for the agonist--adrenoceptor interaction.This work was supported by a grant from the Deutsche ForschungsgemeinschaftParts of this work were presented at the Spring Meetings of the German Pharmacological Society (Wiemer et al. 1978, 1981 b)Herrn Professor Dr. med. Hans Herken, Pharmakologisches Institut der Freien Universität Berlin, zum 70. Geburtstag gewidmet.     

Alternative molecular interpretations of binding curves: compelling competition?

A drug which increases the K_d of a radioligand without altering its B_max has a competitive interaction with the receptors. Although such data occur most commonly in simple situations in which the drug and radioligand bind reversibly to a common binding site without altering the receptors in other ways,Antonio DeBlasi andHarvey Motulsky point out that similar data can also be obtained in more complicated situations.     

Physical characterization of carteolol: Eudragit® L binding interaction

Eudragit® L 30D was used as a carrier to prepare carteolol polymeric complexes in order to obtain controlled release dosage forms. The polyanionic form of the polymer, neutralized at different degrees, reacts readily with carteolol hydrochloride to give water-insoluble complexes. Carteolol complexes were characterized by differential scanning calorimetry, IR, ¹H- and ¹³C-NMR spectroscopy. In fact, results indicated that there were intermolecular associations between the polymer and the drug consisting in ammonium salt interactions. Maximum carteolol content was found to be 22% in the complexes.     

Characterization of thymoquinone binding to human α₁-acid glycoprotein

Thymoquinone (TQ) is the main bioactive component isolated from Nigella sativa essential oil and seeds and has been used for the treatment of inflammations, liver disorders, arthritis, and is of great importance as a promising therapeutic drug for different diseases including cancer. This paper reports the first experimental evidence on binding of TQ to human α(1)-acid glycoprotein (AGP), an important drug-binding glycoprotein in human plasma, which affects pharmacokinetic properties of various therapeutic agents. The interaction of TQ with AGP has been characterized by Fourier transform infrared (FTIR) and fluorescence spectroscopy, as well as by molecular docking experiments. FTIR spectroscopy showed that the binding of TQ to AGP slightly increases its thermal stability and shifts the existence of a molten globule-like state observed in a previous study to higher temperature. The binding constants K(a); the number of binding sites n; and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy. Fluorescence quenching experiments indicated that TQ binding involves hydrophobic interactions and to a lower extent hydrogen bonds, in agreement with molecular docking experiments. The data on binding ability of TQ to AGP represent basic information for the TQ pharmacokinetics such as drug metabolism and distribution in the body.     

The recovery of α-adrenoceptor function and binding sites after phenoxybenzamine

Summary The recovery of peripheral -adrenoceptor function and binding sites was studied in male New Zealand white rabbits after treatment with the irreversible adrenoceptor antagonist phenoxybenzamine. Phenoxybenzamine (5 mg/kg) was administered intravenously and the animals studied 30 min to 12 days later. Pressor dose response curves to intravenous phenylephrine, noradrenaline and guanabenz were constructed in vivo in conscious animals. The contractile response of abdominal aorta and renal artery to phenylephrine and noradrenaline was examined in vitro and the recovery of specific prazosin and clonidine binding to spleen membranes investigated in radioligand binding studies.The half life (t _1/2) for recovery of maximum pressor response in vivo ranged from 0.9±0.2 days for phenylephrine to 1.4±0.1 days for guanabenz. The t _1/2 for recovery of ED₅₀ was not significantly different to t _1/2 for recovery of maximum pressor response and ranged from 0.8±0.2 days for noradrenaline to 1.3±0.3 days for phenylephrine.Half life for recovery of maximum response and EC₅₀ in the isolated tissues was similar to that obtained in vivo for recovery of pressor responses and ranged from 0.4±0.1 days for the EC₅₀ of noradrenaline in the renal artery to 1.2±0.6 days for maximum response to phenylephrine in the abdominal aorta.The rate of recovery of specific clonidine binding did not differ significantly from the rate of recovery of pressor responses to the ₂-selective agonist guanabenz. t _1/2 for maximum number of specific clonidine binding sites, B _max was 1.6±0.9 days. However t _1/2 for recovery of specific prazosin binding was significantly longer than recovery of responses to phenylephrine and noradrenaline, t _1/2 for B _max was 3.6 ±0.1 day.     

Kinetic binding assays for the analysis of protein–ligand interactions

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Autoradiographic analysis of cannabinoid receptor binding and cannabinoid agonist-stimulated [35S]GTPγS binding in morphine-dependent mice

The present study was designed to test the possible existence of changes in brain cannabinoid receptors in morphine-dependent mice. To this end, we compared cannabinoid receptor binding and WIN 55,212-2-stimulated [³⁵S]guanylyl-5′-O-(γ-thio)-triphosphate ([³⁵S]GTPγS) binding in several brain regions of mice chronically exposed to morphine or saline. The existence of opiate dependence in morphine-injected mice was assessed by analyzing the well-known jumping behavior induced by the blockade of opioid receptors with naloxone, whereas these animals were unresponsive to the blockade of cannabinoid receptors with SR141716. The different structures analyzed exhibited similar cannabinoid receptor binding levels in morphine-dependent and control mice, with the only exception of the globus pallidus, which exhibited a very small, but statistically significant, increase. In addition, the activation of cannabinoid receptors with WIN 55,212-2 increased [³⁵S]GTPγS binding in most of the structures examined. The increase was of similar magnitude in morphine-dependent and control mice, except in the substantia nigra, where morphine-dependent mice exhibited lesser [³⁵S]GTPγS binding levels in basal conditions, although a significantly higher WIN 55,212-2-stimulated binding. Other structures, such as the central gray substance, where there was a poor agonist-induced stimulation in control mice, exhibited, however, higher levels of WIN 55,212-2-stimulated [³⁵S]GTPγS binding in morphine-dependent mice, whereas these animals tended to exhibit a higher [³⁵S]GTPγS binding levels in basal conditions, although a lesser and not statistically significant WIN 55,212-2-stimulated binding, in the deep layers of the cerebral cortex. Thus, the data support the potential existence of a specific effect of morphine in the coupling of cannabinoid receptors to GTP-binding proteins, rather than on receptor binding, although this was observed only in the substantia nigra and central gray substance.     

Characterisation of human recombinant somatostatin receptors. 2. Modulation of GTPγS binding

G protein activation by somatostatin (somatotropin release inhibiting factor, SRIF), cortistatin (CST) and analogues of these neuropeptides was investigated at human somatostatin receptor subtypes 1-5 (sst1-5) stably expressed in CCL39 Chinese hamster lung fibroblast cells by measuring agonist-stimulated [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTPgammaS) binding. [35S]GTPgammaS binding was assessed in the presence of 100 mM NaCl and 1 microM GDP, although higher Emax and/or pEC50 values may have been obtained under other conditions, but at the expense of lower absolute stimulation or signal/noise ratio. SRIF14 stimulated [35S]GTPgammaS binding to 162, 220, 148 and 266% of control levels via sst2, sst3, sst4 and sst5 receptors, respectively. At sst1 receptors, SRIF14 produced only a limited stimulation (Emax 115%). Hence sst1 receptors were not subjected to further [35S]GTPgammaS binding experiments. [35S]GTPgammaS binding assays were then performed with sst2-5 receptors. Most of the peptide analogues stimulated [35S]GTPgammaS binding in sst2-5 receptor-expressing cells. BIM 23056 behaved as an antagonist on SRIF14-induced [35S]GTPgammaS binding with an apparent pKBs of 6.33 and 5.84 at hsst3 and hsst5 receptors respectively, whereas neither agonism nor antagonism could be shown (at 1 microM) at sst2 or sst4 receptors. The effect at sst5 receptors was not surmountable and needs further investigations. The so-called "antagonist" SA, was devoid of antagonist activity at sst2 or sst3 receptors, whereas it was almost a full agonist at sst4 and sst5 receptor-mediated [35S]GTPgammaS binding. The [35S]GTPgammaS-binding profiles of hsst2-5 receptors were compared with their respective radioligand binding profiles. For sst4 and sst5 receptors, the rank order of affinity of all tested radioligands correlated highly significantly with [35S]GTPgammaS binding (r = 0.814-0.897). At sst3 receptors, [35S]GTPgammaS binding correlated somewhat less with binding profiles obtained with [125I][Tyr10]CST14 and [125I]CGP 23996 than with [125I]LTT-SRIF28 (r = 0.743, 0.757 and 0.882, respectively). At sst2 receptors, [35S]GTPgammaS binding correlated with [125I]LTT-SRIF28, [125I]CGP 23996 and [125I][Tyr3]octreotide binding profiles (r = 0.596-0.699), but not with [125I][Tyr10]CST14 binding. The present [35S]GTPgammaS binding data combined to previous radioligand binding results obtained in cells expressing human SRIF receptors, suggest that at any given receptor, agonists' rank orders of potency (not to mention absolute affinity values which vary profoundly) are not as strictly ordered as may be anticipated. We are investigating these aspects further by analysing additional signalling pathways.     

Effect of di-n-propylacetate on the ‘binding’ of GABA to a synaptosome-enriched fraction of rat cerebral cortex

The effect of di-n-propylacetate (DPA) on the binding of -aminobutyric acid (GABA) to a synaptosome-enriched fraction of rat cerebral cortex has been examined using differential centrifugation and double-isotope liquid scintillation spectrometry. DPA at 10^-4 M caused a slight decrease in GABA binding. This effect could explain in part the in vivo anticonvulsant and behavioral effects of this drug when administered to animals in high systemic doses.     

Enhancement of δ- but not μ-opiate agonist binding by calcium

Summary Present evidence for distinction of 2 types of opiate receptor sites in rat brain homogenates originates from different relative affinities of morphine-like alkaloids and enkephalins to -or enkephalin and - or morphine-receptor sites. We now report that Ca²⁺ in a physiological dose range (0.5–3 mM) enhances the binding of ³H-enkephalin in hypotonically treated rat brain membranes, whereas specific binding of ³H-morphine-like alkaloids is not affected. Furthermore, the potency of [d-Ala², d-Leu⁵]-enkephalin to inhibit [³H]-diprenorphine and [³H]-ethylketazocine binding increased in the presence of Ca²⁺, whereas an increase in potency of [d-Ala², d-Leu⁵]-enkephalin to inhibit binding of -receptor ligands was not observed. Kinetic analysis revealed that Ca²⁺ decreased the rate of dissociation of [d-Ala², d-Leu⁵]-enkephalin without affecting the rate of association, thereby increasing the affinity. However, in saturation binding studies, performed in diencephalic membranes, in which [d-Ala², d-Leu⁵]-enkephalin binds predominantly to -receptors, Ca²⁺ also increased the binding affinity of [³H]-[d-Ala², d-Leu⁵]-enkephalin. Double reciprocal analysis suggested a mixed competitive-noncompetitive type of inhibition of [d-Ala², d-Leu⁵]-enkephalin binding by dihydromorphine. Thus, the interactions of - and -opiate ligands with -receptors may involve topographically different, but closely related binding sites, located on a single receptor molecule.Abbreviations DADL [d-Ala², d-Leu⁵]-enkephalin - DHM dihydromorphine - met-enkephalin methionine-enkephalin - leu-enkephalin leucine-enkephaline - FK 33-824 [d-Ala², MePhe⁴, Met(O)-ol]-enkephalin - EGTA ethyleneglycol-bis-(-aminoethylether) N, N'-tetraacetic acid - TRIS Tris (hydroxymethyl)-aminomethan     

Use of immunoturbidimetry to detect venom–antivenom binding using snake venoms

IntroductionImmunoturbidimetry studies the phenomenon of immunoprecipitation of antigens and antibodies in solution, where there is the formation of large, polymeric insoluble immunocomplexes that increase the turbidity of the solution. We used immunoturbidimetry to investigate the interaction between commercial snake antivenoms and snake venoms, as well as cross-reactivity between different snake venoms.MethodsSerial dilutions of commercial snake antivenoms (100 μl) in water were placed in the wells of a microtitre plate and 100 μl of a venom solution (50 μg/ml in water) was added. Absorbance readings were taken at 340 nm every minute on a BioTek ELx808 plate reader at 37 °C. Limits imposed were a 30 minute cut-off and 0.004 as the lowest significant maximum increase. Reactions with rabbit antibodies were carried out similarly, except that antibody dilutions were in PBS.ResultsMixing venom and antivenom/antibodies resulted in an immediate increase in turbidity, which either reached a maximum or continued to increase until a 30 minute cut-off. There was a peak in absorbance readings for most Australian snake venoms mixed with the corresponding commercial antivenom, except for Pseudonaja textilis venom and brown snake antivenom. There was cross-reactivity between Naja naja venom from Sri Lanka and tiger snake antivenom indicated by turbidity when they were mixed. Mixing rabbit anti-snake antibodies with snake venoms resulted in increasing turbidity, but there was not a peak suggesting the antibodies were not sufficiently concentrated. The absorbance reading at pre-determined concentrations of rabbit antibodies mixed with different venoms was able to quantify the cross-reactivity between venoms. Indian antivenoms from two manufacturers were tested against four Sri Lankan snake venoms (Daboia russelli, N. naja, Echis carinatus and Bungarus caeruleus) and showed limited formation of immunocomplexes with antivenom from one manufacturer.DiscussionThe turbidity test provides an easy and rapid way to compare and characterise interactions between antivenoms and snake venoms.     

Evaluation of molecular modeling of agonist binding in light of the crystallographic structure of an agonist-bound A₂A adenosine receptor

Molecular modeling of agonist binding to the human A(2A) adenosine receptor (AR) was assessed and extended in light of crystallographic structures. Heterocyclic adenine nitrogens of cocrystallized agonist overlaid corresponding positions of the heterocyclic base of a bound triazolotriazine antagonist, and ribose moiety was coordinated in a hydrophilic region, as previously predicted based on modeling using the inactive receptor. Automatic agonist docking of 20 known potent nucleoside agonists to agonist-bound A(2A)AR crystallographic structures predicted new stabilizing protein interactions to provide a structural basis for previous empirical structure activity relationships consistent with previous mutagenesis results. We predicted binding of novel C2 terminal amino acid conjugates of A(2A)AR agonist CGS21680 and used these models to interpret effects on binding affinity of newly synthesized agonists. d-Amino acid conjugates were generally more potent than l-stereoisomers and free terminal carboxylates more potent than corresponding methyl esters. Amino acid moieties were coordinated close to extracellular loops 2 and 3. Thus, molecular modeling is useful in probing ligand recognition and rational design of GPCR-targeting compounds with specific pharmacological profiles.     

Effects of ohmefentanyl stereoisomers on phosphorylation of cAMP-response element binding protein in cultured rat hippocampal neurons

AIM: To define the effects and signal pathways of ohmefentanyl stereoisomers [(-)-cis-(3R,4S,2'R) OMF (F9202), (+)-cis-(3R,4S,2'S) OMF (F9204), and (-)-cis-(3S,4S,2'R) OMF (F9203)] on the phosphorylation of cAMP-response element binding protein (CREB) in cultured rat hippocampal neurons. METHODS: The effects of the three OMF stereoisomers and morphine (Mor) on cAMP accumulation and CREB phosphorylation were monitored by radioimmunoassay and Western blot analysis, respectively. RESULTS: The three OMF stereoisomers and Mor could all partially inhibit forskolin-stimulated (25μmol/L, 15min) cAMP accumulation in a dose-dependent manner and this effect could be reversed by naloxone. F9202, F9204, and Mor could significantly increase CREB phosphorylation from 2.88 to 3.59 folds over control levels after 30-min exposure. This effect was reversed by naloxone, but F9203 failed to increase CREB phosphorylation. KN-62 and staurosporine significantly blocked the opioidsinduced CREB phosphorylation, while H-89 and P     

Effects of imidazoline binding site ligands on the growth and viability of clonal pancreatic β-cells

Pancreatic beta-cells express imidazoline binding sites which play a role in the regulation of insulin secretion, but it is not known whether ligands for these sites also affect other aspects of beta-cell physiology. In the present study, we have investigated the effects of a range of imidazoline reagents on the growth and viability of clonal pancreatic beta-cells (RINm5F and HIT-T15). Three imidazoline compounds (idazoxan, phentolamine and antazoline) were found to cause marked inhibition of beta-cell growth in a time and concentration dependent manner. Idazoxan was the most potent of these with as little as 0.5 microM causing a significant decrease in beta-cell viability (EC50 approximately 10 microM). All three imidazolines also decreased the viability of clonal beta-cells in parallel with their inhibitory effects on cell growth. These effects were not reproduced by any of a wide-range of other imidazoline compounds, including effective insulin secretagogues such as efaroxan and RX821002. The effects of the three ligands did not correlate with their relative potencies for binding to any of the well-characterised imidazoline binding sites nor to alpha2-adrenoceptors. In addition, the inhibitory responses were not antagonised by other imidazoline binding site ligands. The inhibitory effects of idazoxan on the growth of RINm5F and HIT-T15 beta-cells required as little as 3-h exposure to the imidazoline and were not readily reversible when the reagent was removed. Reductions in growth rate were accompanied by marked alterations in the morphology of the cells, which could be detected before loss of viability. Cells exposed to phentolamine showed the characteristic features of apoptosis in that the nuclei were condensed (as judged by acridine orange staining) and electrophoresis of DNA revealed the presence of oligonucleosomal fragmentation. These changes could not be detected in cells exposed to idazoxan despite the more profound reduction in viability induced by this agent. We conclude that a sub-group of imidazoline compounds can exert profoundly detrimental effects on the growth and viability of clonal beta-cells but that these effects do not correlate with their binding affinity at imidazoline binding sites or alpha2-adrenoceptors.     

The water binding behavior of κ-Carrageenan determined by three different methods

κ-Carrageenan is a biopolymer extracted from red seaweeds which has been in the focus of pharmaceutical development for many years. Most applications make use of the large water binding capacity of κ-carrageenan. The primary limitation of κ-carrageenan is the variation in the substance quality. Therefore, the water binding capacity of different κ-carrageenan products was investigated by dynamic vapor adsorption, freezing and non-freezing bound water and water retention value. The κ-carrageenans were observed to have a higher water binding capacity than microcrystalline cellulose (MCC) in all three methods. The amount of adsorbed water is similar for all carrageenans. Differences between the carrageenan types (κ, ι, and λ) were remarkable for the freezing bound water and centrifugation bound water as well as between the κ-carrageenans of different suppliers.