Osmotic effectors and DNA structure: effect of glycine on precipitation of DNA by multivalent cations

We have investigated the effect of glycine (an organic osmolyte) on DNA precipitation induced by spermine4+, spermidine3+ and Tb3+ addition, using circular dichroism (CD), UV spectroscopy (UV), and electric linear dichroism (ELD) techniques. DNA precipitation by the three compounds is perturbed by glycine: more spermine4+, spermidine3+ and Tb3+ must be added to obtain the same extent of precipitation as compared to the behaviour in absence of this organic osmolyte. It seems that glycine has a general effect on the DNA environment. Calculations based on experimental results and Manning's counterion condensation theory show that glycine could modify the electrostatic environment of DNA as a consequence of a change in dielectric constant.

Differential solubilization of lipids along with membrane proteins by different classes of detergents

Membrane proteins are typically extracted by detergent concentrations of 0.5-2.0%, using detergent/protein ratios of 1:1 to 3:1. We have compared the ability of 14 different detergents from seven different structural and ionic classes, at a concentration of 2.0% and a detergent/protein ratio of 2:1, to extract an integral membrane protein (the serotonin 5-HT1A receptor) in active form and have observed profound differences in both lipids and proteins. All extracts were freed from detergents and dialyzed to form vesicles containing 95-100% of the extracted lipids, prior to [3H]8-hydroxy-2-(N,N-di-n-propylamino)tetralin ([3H]8-OH-DPAT) binding. The most efficient detergents in extracting active 5-HT1A receptor protein were the zwitterionic 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and 3-[(cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate (CHAPSO), followed by the neutral n-dodecyl-beta-D-maltoside. Zwitterionic detergents also produced the highest solubilized lipid/protein ratio (3.0 and 2.5, respectively) and in general the relative amounts of extracted lipids and proteins followed inverse profiles. Thus, hydrophobic detergents such as Tritons (with critical micelle concentrations similar to CHAPS) and Thesit (structurally similar to Lubrol) extracted the most protein, but relatively little lipid (ratios of less than 0.2) and very little active 5-HT receptor. Dramatic differences were also observed in the ratios of individual lipids extracted by the same concentrations of different detergents and resolved by high-performance thin-layer chromatography. For example, galactosylceramide (GalCer) content ranged from 2.7% (CHAPSO) to 13.4% (sodium cholate) of the total lipid extract and cholesterol ranged from 0% (digitonin) to 17.9% (Triton X-100). The detergent-extractability profile for phosphatidylethanolamine (PE) (range 15-40% of total lipid) paralleled that of phosphatidylinositol (PI) (range 4-10%), but was inverse to that for GalCer and cholesterol. Detergent-extractability profiles for phosphatidylcholine (PC) and phosphatidylserine (PS) also followed inverse profiles, with zwitterionic detergents giving high PS/PC and high PE/PC ratios (approximately 2:1), whereas the Tritons and digitonin gave ratios of 1:2. We believe that differential solubilization of lipids, as well as proteins, by detergents is important for the biological activity of the extracted proteins, and lipid extractability should be taken into account when purifying membrane proteins.

Binding studies of cationic thymidyl deoxyribonucleic guanidine to RNA homopolynucleotides

Deoxyribonucleic guanidine is a potential antisense agent that is generated via the replacement of the negative phosphodiester linkages of DNA [--O--(PO2-)--O--] with positively-charged guanidinium (g) linkages [--NH--C(==NH2+)--NH--]. A pentameric thymidyl deoxyribonucleic guanidine molecule [d(Tg)4T-azido] has been shown to base pair specifically to poly(rA) with an unprecedented affinity. Both double and triple strands consisting of one and two equivalents of d(Tg)4T-azido paired with one equivalent of poly(rA) are indicated by thermal denaturation experiments. At an ionic strength of 0.22, the five bases of d(Tg)4T-azido are estimated to dissociate from a double helix with poly(rA) at > 100 degrees C! The effect of ionic strength on thermal denaturation is very pronounced, with stability greatest at low ionic strengths. The method of continuous variation indicates that there is an equilibrium complex with a molar ratio of d(Tg) to r(Ap) or d(Ap) of 2:1. Based on this evidence, models of the structures of d(Tg)9T-azido bound to r(Ap)9A are proposed.

Neutralization of the positive charges of surfactant protein C. Effects on structure and function

Pulmonary surfactant protein C (SP-C) is a small, extremely hydrophobic peptide with a highly conservative primary structure. The protein is characterized by two adjacent palmitoylated cysteine residues, two positively charged residues (one arginine residue and one lysine residue) in the N-terminal region, and a long hydrophobic stretch. SP-C enhances the adsorption of phospholipids into an air-water interface. To determine the importance of the positively charged residues, we carried out experiments with natural porcine SP-C and modified porcine SP-C (SP-Cm) in which the positive charges had been blocked by phenylglyoxal. Circular dichroism experiments showed that SP-Cm had an increased content of alpha-helix. Natural SP-C, but not SP-Cm, catalyzed insertion of phospholipids into a monolayer at the airwater interface. This reduced insertion was due to a strong reduction of binding of phospholipid vesicles to the monolayer. The insertion catalyzed by the natural porcine SP-C was decreased by an increased pH of the subphase. In contrast to natural SP-C, SP-Cm induced lipid mixing between phospholipid vesicles. The extent of lipid mixing was a function of the SP-C content. We conclude that the positively charged residues of SP-C are important for the binding of phospholipid vesicles to the monolayer, a process that precedes the insertion of phospholipids into the monolayer.

Aminium cation radical mechanism proposed for monoamine oxidase B catalysis: are there alternatives?

1. The interaction of bovine liver mitochondrial monoamine oxidase B (MAO B) with a series of benzylamine analogues was investigated to provide mechanistic information relative to the proposed cation radical mechanism and to provide information on the structural requirements of the substrate binding site. 2. Steady-state kinetic analysis of MAO B with 11 ring-substituted benzylamine analogues showed substitution does not alter the reaction pathway. All amine analogues tested exhibit sizeable deuterium kinetic isotope effects. 3. Anaerobic stopped-flow kinetic studies showed (1) C-H bond cleavage is rate-limiting in enzyme-bound flavin reduction and (2) that no specially detectable flavin radicals are observed. 4. The binding affinity of para-substituted benzylamine analogues to MAO B increased as the hydrophobicity of the substituent increased. In contrast, meta-substitution of the ring showed reduced affinity with an increase in the van der Waals volume of the substituent. 5. The rate of enzyme reduction by para-substitution exhibited a strong negative dependence with the Taft (Es) steric value of the substituent. In contrast, the rate of enzyme reduction by meta-substituted benzylamines is independent of the nature of the substituent. 6. para-Substituted N,N-dimethylbenzylamine analogues are not substrates for MAO B but are competitive inhibitors of benzylamine oxidation with a weaker affinity with increasing van der Waals volume of the substituent. In contrast, meta-substituted N,N-dimethyl benzylamine analogues are weak substrates for MAO B with oxidation occurring exclusively at the benzyl carbon. 7. The consequences of these results on the possible mechanisms (aminium cation radical, H abstraction, and nucleophilic mechanism) for C-H bond cleavage proposed for MAO B are discussed.

Haemoprotein-mediated metabolism of enamines and the possible involvement of one-electron oxidations

1. Microsomal metabolism of 1-benzylpiperidine (1-BP), its cis-2,6-dimethyl (cis-2,6-DMBP), 4,4-dimethyl (4,4-DMBP), and alpha, alpha-dimethyl (alpha, alpha-DMBP) analogues, and phencyclidine (PCP) has been studied to assess the involvement of P450 oxidation of the enamine tautomers of the initial endocyclic iminium metabolites. 2. The selective prevention by cyanide of the metabolite production of 1-benzyl-3-piperidone but not 1-benzyl-3-piperidinol from 1-BP is consistent with the enamine as the source of the 3-one metabolite. 3. The parent amines and particularly the independently prepared iminium species induced a pattern of metabolism-dependent irreversible inactivation of P450 benz-phetamine demethylase activity, consistent with involvement of enamine C-3 oxidation in the inactivation process. 4. Substrate activity of the endocyclic enamines and alpha-aminoketones (presumably the enol-enamine tautomers) for horseradish peroxidase under conditions where simple aliphatic amines display no activity is consistent with metabolic one-electron oxidations of the enamines.

Radical intermediates during degradation of lignin-model compounds and environmental pollutants: an electron spin resonance study

1. I discuss the following aspects of Phanerochaete chrysosporium ligninase, the enzyme that has been shown to degrade a number of lignin-model compounds, and environmentally significant polycyclic aromatic hydrocarbons and polychlorinated phenols. 2. The primary mode of oxidation involves formation of a cation radical, which undergoes either hydrolysis or carbon-carbon bond cleavage. 3. In the presence of reducing substrate such as oxalic acid, ligninase has reductive activity that has been shown to be responsible for radical-mediated degradation of halogenated chemicals. 4. Electron spin resonance technique can be used to monitor the cation radical and other radical formation during ligninase-mediated degradation of lignin-model compounds and other chemicals.

Radical cations of benzo[a]pyrene and 6-substituted derivatives: reaction with nucleophiles and DNA

1. Oxidation of benzo[a]pyrene (BP) by I2 in the presence of AgClO4 in benzene generates the BP.+ClO4-.AgI complex. This same method was used to produce radical cations from 6-FBP, 6-ClBP, 6-BrBP and 6-CH3BP. 2. Reaction of the BP, 6-FBP, 6-ClBP and 6-BrBP radical cation perchlorates with H2O produced BP 1,6-, 3,6- and 6,12- dione, whereas 6-CH3BP.+ClO4-.AgI yielded 6-CH2OHBP. 3. When BP.+ClO4-.AgI and 6-FBP.+ClO4-.AgI were reacted with NaOAc in H2O/CH3CN (9:1), 6-OAcBP was formed, in addition to the quinones. In the case of 6-ClBP.+ClO4-.AgI, a small amount of 1-OAc-6-ClBP and 3-OAc-6-ClBP was formed in addition to the diones, whereas for 6-BrBP and 6-CH3BP the reaction products were BP diones and 6-CH2OHBP respectively. 4. These results confirm the localization of charge in the BP.+ at C-6, followed by C-1 and C-3. 5. The reaction of BP with NOBF4 in CH2Cl2 produced BP.+BF4-, radical cation free of complexation with inorganic salts. 6. Reaction of BP.+BF4- with DNA produced the depurinating adducts BP-6-C8Gua, BP-6-C8dGua and BP-6-N7Gua.

Fragmentation reactions of aromatic cation radicals: a tool for the detection of electron transfer mechanisms in biomimetic and enzymatic oxidations

1. Mechanistic criteria, based on the side-chain fragmentation reactions of aromatic cation radicals, involving the cleavage of a beta bond (i.e. C-H, C-Si and C-S) have been developed for the detection of electron transfer mechanisms in oxidative processes of alkylbenzenes and aromatic sulphides. 2. For benzylic oxidations, the distinction between electron transfer (ET) and hydrogen atom transfer mechanism (HAT) has been based: (a) on studies of intramolecular selectivity, which, with appropriate substrates (5-Z-1,2,3,-trimethylbenzenes and 4-Z-1,2-dimethylbenzenes, where Z = OMe, alkyl), turns out to be much higher in ET than in HAT processes; and (b) on products studies concerning the reactions of bicumyl and benzyltrimethylsilanes since in these systems, the nature of products can be significantly different for ET and HAT mechanisms. 3. These criteria have been applied to the reactions of alkylbenzenes with an NO3 radical (shown to be an ET process) as well as to the microsomal and biomimetic (by iron porphyrins in the presence of PhIO) side-chain oxidation of the same compounds, where the mechanistic probes have suggested a HAT mechanism, with the exception of the biomimetic oxidation of 4-methoxybenzyltrimethylsilane in CH2Cl2-H2O-MeOH, which probably occurs by an ET mechanism. 4. For the enzymatic and biomimetic oxidation of aromatic sulphides an oxygen transfer is suggested, since, with cumyl phenyl sulphide and 4-methoxybenzyl phenyl sulphide, these reactions lead exclusively to the corresponding sulphoxides and sulphones, whereas the same substrates, in genuine ET reactions, form cation radicals which undergo C-H and C-S bond cleavage. 5. An oxygen transfer mechanism is also likely in the biomimetic and enzymatic oxidations of sulphoxides since in these reactions 4-methoxybenzyl phenyl sulphoxide is exclusively converted to sulphone, whereas in ET reactions it forms only C-S bond cleavage products.

Porphyrin pi-cation and protein radicals in peroxidase catalysis and inhibition by anti-thyroid chemicals

1. Thyroid peroxidase (TPO) catalyses the iodination and phenolic coupling reactions in the biosynthesis of thyroid hormones. 2. The two-electron oxidation of TPO by H2O2 produces an oxoferryl porphyrin pi-cation radical compound I that isomerizes spontaneously to a form of compound I that contains an oxoferryl haem and the second oxidizing equivalent as an amino acid radical. 3. The pi-cation radical compound I is the catalytic species that effects iodide ion oxidation and the protein radical compound I is most likely the catalytic species that catalyses coupling. 4. Methimazole, a therapeutic, anti-hyperthyroid drug, is a suicide substrate for TPO and effects irreversible inactivation by TPO-mediated S-oxygenation to a reactive sulphenic acid that binds covalently to the prosthetic haem. 5. Sulphamethazine and other arylamines containing electron-withdrawing substituents inhibit TPO compound I-mediated reactions by reversible, mixed-type inhibition. 6. Ethylenethiourea, a fungicide metabolite, blocks TPO-mediated iodination by reacting with the catalytic iodinating species as an alternate substrate. 7. Resorcinol and related dietary flavonoids are suicide substrates for TPO and act by covalent binding to amino acid residues, presumably those radical sites present in the compound I isomer. 8. Nitrosobenzene, a known radical-trapping agent, blocks TPO-mediated coupling but not iodination or phenolic oxidations presumably by interception of the 3,5-diiodotyrosyl radical species generated during the coupling reaction.

Cation radicals of organosulphur compounds

1. Biological and biomimetic oxidations of thioethers are reviewed. 2. gamma-Radiolysis, pulse radiolysis, photochemical, chemical, and electrochemical methods for generating sulphur cation radicals are discussed and exemplified. 3. The major reactions of sulphur cation radicals: nucleophilic attack, electron transfer, decarboxylation, reaction with O2, C-S, C-C, and alpha-C-M bond cleavages, sulphur abstraction, and rearrangements are presented.

Radical cation intermediates in N-dealkylation reactions

1. A number of mechanistic possibilities exist for P450-catalysed N-dealkylation and have been considered over the years, including C- and N-hydroxylation and sequential electron transfer (SET). With peroxidases the evidence strongly favours SET and free radicals can be detected. Any mechanism must account for lack of incorporation of label from H218O into product by P450s and the high kinetic deuterium isotope effects that are seen in N-dealkylation reactions catalysed by peroxidases but not P450s. 2. Several lines of evidence support a role for SET in P450 amine oxidations, including Hammett analysis, products of dihydropyridine oxidations, and products of mechanism-based inhibition by strained cycloalkylamines. 3. The hypothesis was considered that the P450s act via base catalysis to deprotonate the aminium radical generated by SET, since the pKa has been estimated to be approximately 9. Dihydropyridine aminium radicals have low pKa (< 4) and are generally considered to have considerable kinetic acidity. None of the haemoproteins under consideration (including the peroxidases and haemoglobin) showed high kinetic hydrogen isotope effects for the oxidation of [4-2H]- or [4-3H]-labelled 1,4-dihydropyridines. These results are consonant with the view that P450s catalyse the deprotonation of N,N-dialkylaniline aminium radicals. 4. Since low isotope effects were seen with biomimetic metalloporphyrin models as well as P450s, the deprotonation is attributed to the (FeO)2+ entity, expected to be a strong base, and not the apoprotein. Thus, the FeO moiety of peroxidases is shielded, consistent with evidence by others that SET occurs through the porphyrin edge. Both P450s and peroxidases catalysed the oxidative N-demethylation of aminopyrine and N,N-dimethylaminothioanisole; however, only the peroxidases generated the stable coloured aminium radicals. 5. The rates of N-demethylation of variously para-substituted N,N-dimethylanilines can be used to undertake Hammett or Marcus analysis. The former yields rho = -0.6 and the latter an apparent E1/2 of approximately 1.8 for the formal (FeO)3+ entity of P4502B1. 6. Even in the oxidation of N,N-dialkylanilines, a finite rate of N-oxidation is seen (approximately 0.1% of N-dealkylation). The simplest paradigm has N-oxygenation and N-dealkylation both proceeding from a common aminium radical intermediate.

Central role of radical cations in metabolic activation of polycyclic aromatic hydrocarbons

1. Development of the chemistry of polycyclic aromatic hydrocarbon (PAH) radical cations has provided evidence that these intermediates play a major role in the metabolism of PAHs by P450 and in their binding to DNA. 2. Fluoro substitution of benzo[a]pyrene (BP) represents a suitable probe for studying mechanisms of oxygen transfer in the P450-catalysed formation of quinones and phenols from BP. Formation of BP-1,6-, -3,6- and -6,12-dione from the metabolism of 6-fluoroBP (6-FBP) is mediated by the intermediate 6-FBP+. Similarly, metabolism of 1-FBP and 3-FBP by rat liver microsomes produces BP-1,6-dione and BP-3,6-dione respectively. These results demonstrate that formation of quinones and phenols occurs via an initial electron transfer from BP to P450 and subsequent transfer of oxygen from the iron-oxo complex of P450 to BP. 3. Radical cations also play a major role in the formation of DNA adducts by the potent carcinogens 7,12-dimethylbenz[a]anthracene (DMBA), BP and dibenzo[a,l]pyrene (DB[a,l]P). In the binding of BP both in vitro and in vivo, 80% of the adducts are formed by one-electron oxidation, namely, 8-(BP-6-yl)guanine (BP-6-C8Gua), BP-6-N7Gua and BP-6-N7adenine (Ade), and are lost from the DNA by depurination. For DB[a,l]P, depurinating adducts formed from the radical cation, DB[a,l]P-10-C8Gua, DB[a,l]P-10-N7Gua, DB[a,l]P-10-N7Ade, and DB[a,l]P-10-N3Ade comprise 50% of the total DNA adducts. For DMBA, 99% of the adducts are depurinating adducts formed from the radical cation, 7-CH3BA-12-CH2-N7Gua and 7-CH3BA-12-CH2-N7Ade. 4. In summary, radical cations of PAHs play a major role in both the metabolism and metabolic activation leading to formation of DNA adducts that are critical in the mechanism of tumour initiation.

Mechanisms involved in iontophoretic transport of angiotensin

PURPOSE

The feasibility of using iontophoresis to enhance the permeation rate of a model peptide was investigated in vitro using hairless mouse skin.

METHODS

Angiotensin 2 (AT 2) was employed as a permeant probe, using optimum iontophoresis conditions. A number of physicochemical parameters (donor ionic strength; valence of competitive ions; pH of donor solution) were studied with the aim of exploring the mechanisms involved in the iontophoretic transport through the skin: electrokinetic transport or convective transport. For this purpose, the magnitude of the convective solvent flow was also evaluated by the permeation of (3H) H2O. The interest of pulsed currents for peptide delivery was also investigated and the effect of current density and frequency was studied.

RESULTS

AT 2 transport was found to be enhanced 20-fold in comparison to passive permeation and was found to be proportional to the current density with direct currents as with pulsed currents.

CONCLUSIONS

Although the flux enhancement of ions during iontophoresis is due principally to the electrical potential gradient, secondary effects such as convective solvent flow contribute also to flux enhancement of peptide delivery. This effect is dependent of physicochemical conditions of formulation.

Radiation-induced formation of haematoporphyrin-transients in aqueous solution. A pulse radiolysis study

The radiation-induced formation of some haematoporphyrin (HP) transients in aqueous solution was studied by pulse radiolysis. The OH radicals attack HP (rate constant k = (1.3 +/- 0.2) x 10(10) dm3 mol-1 s-1) and the resulting transients decay with 2k = (2.5 +/- 0.2) x 10(8) dm3 mol-1 s-1. The spectrum of the HP-OH species shows several maxima in the range of 450-850 nm (epsilon 590 = 3880, epsilon 640 = 3850, epsilon 800 = 3670 dm3 mol-1 cm-1). k for one electron reduction of HP (radical anion, HP.-) was determined by a direct eaq- attack on HP (at pH 9.0, k = (1.6 +/- 0.2) x 10(10) dm3 mol-1 s-1) as well as by electron transfer from hydroxyisopropyl radicals to the substrate (at pH 8.6, k = (3.2 +/- 0.1) x 10(8), at pH 3.8, k = (4.0 +/- 0.2) x 10(8), and at pH 2.0, k = (2.1 +/- 0.1) x 10(9) dm3 mol-1 s-1). In slightly alkaline media (pH 8.6 - 9.5) the HP.- transients have main absorption bands at lambda < 450 and 640 nm (epsilon 660 = 7500 dm3 mol-1 cm-1), whereas at pH 2.0 they are at lambda < 430 and 640 nm (epsilon 640 = 8170 dm3 mol-1 cm-1) and 710 nm (epsilon 710 = 8500 dm3 mol-1 cm-1). The one-electron oxidation of HP (formation of HP.+, radical cation) was studied by means of N3. or SO4.- species as electron acceptors. Using N3. at pH 9.5 k (HP + N3.) = (3.2 +/- 0.2) x 10(9) and for the decay 2k = (3.5 x 0.3) x 10(8) dm3 mol-1 s-1 were determined; at pH 3.6, k = (HP + N3.) = (7.1 +/- 0.3) x 10(8) and 2k = (2.6 +/- 0.3) x 10(7) dm3 mol-1 s-1 were found. In the case of SO4.- at pH9.8 a buildup (5.6 +/- 0.3) x 10.7 dm3 mol-1 s-1) was obtained. The spectrum of the HP.+ transients at pH 9.6 possesses several maxima with epsilon 345 = 38,800, epsilon 450 = 2400, epsilon 595 = 2880, and epsilon 660 = 3300 dm3 mol-1 cm-1. The corresponding values at pH 3.8 are epsilon 640 = 2450, epsilon 710 = 2600, and epsilon 780 = 1580 dm3 mol-1 cm-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Photo-CIDNP study of pyrimidine dimer splitting. I: Reactions involving pyrimidine radical cation intermediates

The light-induced splitting of pyrimidine dimers was studied using the electron acceptor anthraquinone-2-sulfonate (AQS) as a photosensitizer. To this end, photochemically induced dynamic nuclear polarization (photo-CIDNP) experiments were performed on a series of pyrimidine monomers and dimers. The CIDNP spectra demonstrate the existence of both the dimer radical cation, which is formed by electron transfer from the dimer to the photoexcited sensitizer AQS*, and its dissociation product, the monomer radical cation. In spectra of 1,1'-trimethylene bridged cis, syn pyrimidine dimers, polarization is observed that originates from a spin-sorting process in the dimer radical pair. This points to a relatively long lifetime of the dimer radical cation involved, which is presumably due to stabilization by the trimethylene bridge. Polarization originating from a dimer radical pair is detected in the spectrum of trans,anti (1,3-dimethyluracil) dimer as well. The spectra of the bridged pyrimidines also demonstrate the reversibility of the dissociation of dimer radical cation into monomer radical cation, which is concluded from the observation of polarization in the dimer as a result of spin sorting in the monomer radical pair.

Novel kinetics in a biomimetic redox reaction involving NADH and tetrazolium salts in aqueous micellar solutions

Aqueous micelles of Triton X-100 are shown to catalyze the redox reaction between NADH and 2-p-iodophenyl-3-p-nitrophenyl-5-phenyltetrazolum chloride (INT) at neutral pH. The reaction exhibits a first-order dependence on NADH when INT is saturating; conversely, when NADH is saturating, the dependence is strictly second-order with respect to INT. The second-order dependence of the reaction on INT is also evident in situations where micelles of a cationic detergent are used in place of Triton X-100. The available kinetic evidence indicates the transient formation of a central complex involving the addition of two molecules of INT and one molecule of NADH to a "site" on the micelle where they are held together until completion of the redox process. However, the reaction does not seem to proceed by successive 1-e- steps, suggesting that the second-order dependence on INT has no bearing on the mechanism of redox process. The transfer of reducing equivalents between NADH and INT is shown to be direct and quantitative, with the redox steps confined to a microenvironment, as in the case of enzymatic NAD(P)H-dependent reactions. A mechanism consistent with the hydridic nature of the migrating hydrogen from the C(4) position of the dihydropyridine nucleus of NADH is proposed, assuming that only one molecule of INT in the central complex participates in the actual redox process and that the other molecule of INT acts as a cocatalyst by way of providing the necessary "basicity" at the reaction site.

Thermodynamics of an intramolecular DNA triple helix: a calorimetric and spectroscopic study of the pH and salt dependence of thermally induced structural transitions

We have characterized thermodynamically the melting transitions of a DNA 31-mer oligonucleotide (5'-GAAGAGGTTTTTCCTCTTCTTTTTCTTCTCC-3') which is designed to fold into an intramolecular triple helix. The first 19 residues fold back on themselves to form an antiparallel Watson-Crick hairpin duplex with a T5 loop. The 3'-terminal seven residues, which are connected to the Watson-Crick hairpin duplex by a second T5 loop, form Hoogsteen interactions in the major groove of the Watson-Crick hairpin. From ultraviolet (UV) melting studies we find that the 31-mer exhibits either one or two transitions, depending on solution conditions. We use pH- and temperature-dependent circular dichroism (CD) to assign the initial and final states associated with each transition. We find that the disruption of the Hoogsteen hairpin is accompanied by a release of protons and an uptake of sodium ions while the disruption of the Watson-Crick hairpin is accompanied by a release of sodium ions with no change in protonation state. From these data, we construct a phase diagram for this intramolecular DNA triple helix as a function of pH, sodium ion concentration, and temperature. We characterize the energetics of each transition using a van't Hoff analysis and differential scanning calorimetry (DSC). Significantly, the DSC data provide a model-independent thermodynamic characterization of the thermally induced transitions of this triplex. By combining the spectroscopic and calorimetric data, we develop a semi-empirical model which describes the state of the 31-mer as a function of pH, sodium ion concentration, and temperature. With this model we successfully predict characteristics of the 31-mer, which are beyond the data which are used in establishing the model (for example, the salt dependence of the apparent pKa of the Hoogsteen strand). This semi-empirical model may serve as a prototype for developing a method to predict the phase diagrams of intramolecular triple helix systems.

Modelling mucoadhesion by use of surface energy terms obtained from the Lewis acid-Lewis base approach. II. Studies on anionic, cationic, and unionisable polymers

Surface energies of carbopol, chitosan, hydroxypropyl cellulose (HPC) and poly(HEMA) were assessed from contact angle and surface tension experiments. The surface energy was considered in terms of an apolar Lifshitz-van der Waals term and a polar acid-base term, which in turn is divided into electron donor and electron receptor (Lewis acid-Lewis base) contributions. Using these surface energy terms the interaction of dry and hydrated polymer with mucin in the presence of either artificial gastric or intestinal fluid, or saline was predicted. The predictions were related to measured forces of detachment. There was a significant difference between the surface energy on dry and hydrated HPC and also for carbopol; for the other polymers either the surface energy of the hydrated material was not detectable, or the effect of hydration was minimal. There were good correlations between mucoadhesive strength and the calculated free energies of interaction between mucin and polymer in the presence of each of the fluids, for each individual polymer. Thus, two trends were observed, one for unionisable and the other for ionisable polymers. It is argued that the increased mucoadhesion seen with ionisable polymers (compared with the predicted value based on results of unionisable polymers) is a direct result of the ionic interaction. No attempt has been made to correct for the ionisation effect, but the surface energy predictions provide insight into the mechanism of the mucoadhesion process. This approach is useful for understanding and predicting interactions between different materials and biological components.

Cancer gene therapy using plasmid DNA: pharmacokinetic study of DNA following injection in mice

The fate of plasmid DNA complexed with cationic lipids delivered intravenously in mice was evaluated at selected timepoints up to 6 months postinjection. Blood half-life and tissue distribution of plasmid DNA and potential expression in tissues were examined. Southern blot analyses of blood indicated that intact plasmid DNA was rapidly degraded, with a half-life of less than 5 min for intact plasmid, and was no longer detectable at 1 hr postinjection. Southern analyses of tissue demonstrated that intact DNA was differentially retained in the lung, spleen, liver, heart, kidney, marrow, and muscle up to 24 hr postinjection. After 7 days, no intact plasmid DNA was detectable by Southern blot analysis; however, the plasmid was detectable by the polymerase chain reaction (PCR) in all tissues examined at 7 and 28 days postinjection. At 6 months postinjection, femtogram levels of plasmid were detected only in muscle. Immunohistochemical analyses did not detect encoded protein in the tissues harboring residual plasmid at 1 or 7 days postinjection.

Reaction of the coordinate complexes of inositol hexaphosphate with first row transition series cations and Cd(II) with calf intestinal alkaline phosphatase

The reaction of alkaline phosphatase (APase) with the complexes of myo-inositol hexakisphosphate (IHP) and various cations at pH 7.2 results in a decrease in activity. Singly, neither IHP nor metal ions induce such changes. IHP-Mn(II) complexes were the least effective. Using the ions of nickel or cadmium, activity was reduced by > 95%. A similar large decrease (> 99%) was seen previously in the reaction of APase with IHP-Cu(II) complexes. With Co(II) and IHP as reactants, the activity was reduced to 10-12% of that of the native enzyme. When the apoprotein, prepared by reaction of the enzyme with either EDTA or 1,10-phenanthroline, was titrated with Co(II), the activity was equal to that resulting from the reaction of the enzyme with IHP-Co(II) complexes. Titration with zinc restored 95% of the original activity. The products are metal-substituted derivatives in which the resident catalytic (A-site) zinc ions, at least, are replaced by the cation of the IHP complex that was used. The rates of such reactions were fastest with the complexes of Cu(II) and Cd(II) (0.12 min-1), less so with Co(II) as the ion (0.056 min-1), and slowest with complexes of nickel and manganese (0.01 min-1). In every case, the rate of reaction, but not its extent of change, was inhibited by zinc ions that reduced rate constants to 0.0014-0.0054 min-1. Magnesium ions had no effect. Likewise, Mn(II), with but one exception, did not affect the reactions. When present along with IHP-Ni(II) complexes, the rate was increased and the enzyme activity further decreased. If Zn(II) was also present, this enhancement was eliminated. All changes in enzyme activity were reversible by treatment with EDTA followed by reconstitution with zinc. Approximately 95% conversion to the original activity could be attained. Reactivation of modified APase preparation also could be attained, in some cases, by pre-incubation with Zn(II) at pH 8. For example, conversion of the Cd(II)-substituted APase to the zinc enzyme was rapid and complete in 15 min. With the Cu(II)-substituted derivative, reactivation was much slower. Incubation with zinc ions had little or no effect on other Me(II)-substituted APase preparations. Co-APase and Cu-APase, prepared from the apoprotein, behaved similarly to their respective "counterpart product" of the appropriate metal ion-exchange reaction. In contrast, Co-APase, but not Cu-APase, could be converted to the zinc enzyme by incubation with IHP-Zn(II) complexes at pH 7.2. The reaction rate of the various metal-substituted APase preparations with EDTA varied with the IHP-Me(II) used in its formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Complexes of ciprofloxacin with metal ions contained in antacid drugs

Simultaneous administration of antacids containing magnesium or aluminium and ciprofloxacin or other quinolones decreases the gastrointestinal absorption of those antibacterial agents. Current speculation about the mechanism of this interaction has focused on drug-cation chelation. The present study was designed to detect the protonation in solutions and the formation of the complex species at the pH levels typical of the gastrointestinal tract. It involves the study of ciprofloxacin in aqueous solutions containing Al3+ and (or) Mg2+ by combining the results of potentiometric and spectroscopic (1H nuclear magnetic resonance) techniques. Calculations were only performed for data in the range 4.5 < pH < 5.5 (pH levels typical of gastrointestinal tract) and the results of both methods are made self-consistent, assuming an equilibrium model including complex species MHL, MLOH (where H2L denotes ciprofloxacin and M is Al3+ or Mg2+); their formation constants are given.

Effect of membrane surface potential on the uptake and the inhibition of cationic compounds in rat intestinal brush-border membrane vesicles and liposomes

The effect of membrane surface potential on the uptake of tryptamine, an organic cation, by rat intestinal brush-border membrane vesicles was investigated. In the presence of an inside-negative K(+)-diffusion potential, the manner of initial uptake of tryptamine appeared to be pH-dependent and the uptake in the acidic medium was lower than that in the neutral medium. Changes in surface potential of brush-border membrane vesicles were monitored using 8-anilino-1-naphthalenesulfonic acid (ANS) and the results suggested that the membrane surface potential (negative charge on the membrane surface) decreased in the acidic medium. A good correlation was observed between the K(+)-diffusion potential-dependent uptake of tryptamine and membrane surface potential monitored by ANS at various pH levels. The uptake of tryptamine by liposomes (large unilamellar vesicles), which contained various amounts of dipalmitoylphosphatidylserine (DPPS), was also examined. The uptake of tryptamine decreased with a decrease of DPPS content in the liposomes, and was correlated with the membrane surface potential monitored by ANS. Moreover, the effect of organic cations on the uptake of tryptamine by intestinal brush-border membrane vesicles was examined. The uptake of tryptamine was inhibited by tetracaine and imipramine. The inhibitory effect of these cations was well correlated with changes in the membrane surface potential in the presence of tetracaine or imipramine. These results suggest that the K(+)-diffusion potential-dependent uptake of tryptamine by intestinal brush-border membrane vesicles is affected by membrane surface potential, and the inhibition of tryptamine uptake originates in changes in the membrane surface potential caused by the organic cations.

Specific heparin preparations interfere with the simultaneous measurement of ionized magnesium and ionized calcium

OBJECTIVE

To determine whether heparin anticoagulants used for analysis of whole blood ionized calcium would influence the measurement of ionized magnesium.

METHODS

The effects of zinc heparin, lithium heparin, and electrolyte-balanced heparin on the simultaneous measurement of ionized magnesium and ionized calcium in serum were determined using ion selective electrodes.

RESULTS

Time-dependent biases in ionized magnesium and calcium concentrations were apparent with zinc heparin but not with lithium or electrolyte-balanced heparin. Ionized magnesium and calcium concentrations were more significantly influenced by volume-dependent changes in zinc heparin potency than with lithium or electrolyte-balanced heparin.

CONCLUSION

Zinc heparin produces a significant positive bias in the simultaneous determination of ionized magnesium and ionized calcium concentrations.

Modeling cation/anion-water interactions in functional aluminosilicate structures

A need for the computer simulation of hydration/dehydration processes in functional aluminosilicate structures has been noted. Full and realistic simulations of these systems can be somewhat ambitious and require the aid of interactive computer graphics to identify key structural/chemical units, both in the devising of suitable water-ion simulation potentials and in the analysis of hydrogen-bonding schemes in the subsequent simulation studies. In this article, the former is demonstrated by the assembling of a range of essential water-ion potentials. These span the range of formal charges from +4e to -2e, and are evaluated in the context of three types of structure: a porous zeolite, calcium silicate cement, and layered clay. As an example of the latter, the computer graphics output from Monte Carlo computer simulation studies of hydration/dehydration in calcium-zeolite A is presented.

Grand canonical Monte Carlo molecular and thermodynamic predictions of ion effects on binding of an oligocation (L8+) to the center of DNA oligomers

Grand canonical Monte Carlo (GCMC) simulations are reported for aqueous solutions containing excess univalent salt (activities a +/- = 1.76-12.3 mM) and one of the following species: an octacationic rod-like ligand, L8+; a B-DNA oligomer with N phosphate charges (8 < or = N < or = 100); or a complex resulting from the binding of L8+ at the center of an N-mer (24 < or = N < or = 250). Simplified models of these multiply charged species are used in the GCMC simulations to predict the fundamental coulombic contributions to the following experimentally relevant properties: 1) the axial distance over which ligand binding affects local counterion concentrations at the surface of the N-mer; 2) the dependence on N of GCMC preferential interaction coefficients, gamma 32MC identical to delta C3/delta C2l a +/-, T, where C3 and C2 are, respectively, the molar concentrations of salt and the multiply charged species (ligand, N-mer or complex); and 3) the dependence on N of SaKobs identical to d in Kobs/d in a +/- = delta (magnitude of ZJ + 2 gamma 32J), where Kobs is the equilibrium concentration quotient for the binding of L8+ to the center of an N-mer and delta denotes the stoichiometric combination of terms, each of which pertains to a reactant or product J having magnitude of ZJ charges. The participation of electrolyte ions in the ligand binding interaction is quantified by the magnitude of SaKobs, which reflects the net (stoichiometrically weighted) difference in the extent of thermodynamic binding of salt ions to the products and reactants. Results obtained here from GCMC simulations yield a picture of the salient molecular consequences of binding a cationic ligand, as well as thermodynamic predictions whose applicability can be tested experimentally. Formation of the central complex is predicted to cause a dramatic reduction in the surface counterion (e.g., Na+) concentration over a region including but extending well beyond the location of the ligand binding site. For binding a cationic ligand, SaKobs is predicted to be negative, indicating net electrolyte ion release in the binding process. At small enough N, -SaKobs is predicted to decrease strongly toward zero with decreasing N. At intermediate N, -SaKobs appears to exceed its limiting value as N-->infinity.

The influence of cations and ionic strength on actin polymerization in the presence/absence of alpha-actinin

The presence of alpha-actinin has little influence on polymerizing actin with regards to the lag phase, rate and amplitude. Rising KCl or MgCl2 concentrations parallel an increase in polymerization rate and a decrease in lag phase for both protein species. The observed overall smaller actin fluorescence amplitudes in the presence of alpha-actinin is due to a higher ratio of free G-actin to F-actin at steady state.

DNA bending by asymmetric phosphate neutralization

DNA is often bent when complexed with proteins. Understanding the forces responsible for DNA bending would be of fundamental value in exploring the interplay of these macromolecules. A series of experiments was devised to test the hypothesis that proteins with cationic surfaces can induce substantial DNA bending by neutralizing phosphates on one DNA face. Repulsions between phosphates in the remaining anionic helix are predicted to result in an unbalanced compression force acting to deform the DNA toward the protein. This hypothesis is supported by the results of electrophoretic experiments in which DNA spontaneously bends when one helical face is partially modified by incorporation of neutral phosphate analogs. Phasing with respect to a site of intrinsic DNA curvature (hexadeoxyadenylate tract) permits estimation of the electrostatic bend angle, and demonstrates that such modified DNAs are deformed toward the neutralized surface, as predicted. Similar model systems may be useful in exploring the extent to which phosphate neutralization can account for DNA bending by particular proteins.

Analytical applications and implications of intramolecular micelle-mimetic ionene aggregates

The synthesis and relevant properties of some cationic polyelectrolytes of the [x,y]-ionene type (i.e., molecules consisting of dimethylammonium charge centers interconnected by alternating alkyl chain segments containing x and y methylene groups) are described. Such hydrophobic ionenes can form intramolecular aggregates and function as micelle-mimetic agents since they mimic the key properties of traditional surfactant micelles (such as hexadecyltrimethylammonium bromide) in many respects. However, the ionenes possess certain important advantages over surfactant micelles. For example, aqueous ionene-containing solutions exhibit much less foaming and analyte molecules can be extracted and recovered from their solutions by use of organic solvents. In this work, some applications of the ionenes in analytical chemistry, such as their use as mobile phase additives for thin-layer chromatographic and capillary electrophoretic separations, as fluorescence enhancement agents, and as a means to catalyze slow spectroscopic derivatization reactions are demonstrated. In addition, other potential advantages concerning the utilization of the micelle-mimetic ionenes in chemical analysis applications are mentioned.

Oligonucleotide-cationic liposome interactions. A physicochemical study

Cationic liposomes are effective in delivering antisense oligonucleotides into cells in culture, but their interactions with the oligonucleotides are poorly understood. We studied the aggregation and fusion reactions during the formation of cationic lipid/oligonucleotide complexes in solution and their interactions with lipid bilayers. Phosphorothioate oligonucleotides (15-mer) were complexed with cationic liposomes composed of dimethyldioctadecylammonium bromide (DDAB) and dioleoylphosphatidylethanolamine (DOPE) at 8:15 molar ratio or of a commercial formulation DOTAP (N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammoniummethylsul fate), at different ratios with apparent -/+ charge ratios of 0.03-5.6. Mean size of the complexes increased with -/+ ratio so that at charge ratios 0.4-2.0 the size increased by at least an order magnitude due to the oligonucleotide induced aggregation. Resonance energy transfer experiments showed that in addition to aggregation oligonucleotides induced fusion of cationic liposomes, but the fusion was rate-controlled by the initial aggregation step. Rate constants for oligonucleotide induced aggregation were dependent on lipid concentration and were in the range of (0.2-1).10(7) M-1 s-1 and (1-10).10(7) M-1 s-1 for DDAB/DOPE and DOTAP, respectively. Increase in oligonucleotide concentration induced the aggregation and fusion until at high -/+ ratios electrostatic repulsion of negative surfaces inhibited further aggregation and fusion. DOTAP/oligonucleotide complexes did not induce leakage of calcein from neutral EPC liposomes, but did cause leakage at -/+ charge ratios of < 0.7 and > 2.0 from EPC/DOPE liposomes. Also at -/+ charge ratios below 0.8 DOTAP/oligonucleotide complexes induced leaking from negatively charged DPPC/DPPG liposomes. These results indicate that either phosphatidylethanolamine or negative charge are required in the cell membrane for fusion of cationic liposome-oligonucleotide complexes. The ratio of oligonucleotide to cationic lipid is critical in determining the physicochemical properties of the mixture.

Comparison of cell proliferation and toxicity assays using two cationic liposomes

The present study compares different cytotoxicity and cell proliferation assays including cell morphology, mitochondrial activity, DNA synthesis, and cell viability and toxicity assays. CaSki cells were exposed to two cationic liposomal preparations containing dimethyldioctadecyl-ammonium bromide (DDAB), dioleoylphosphatidylethanolamine (DOPE) and a commercial transfection-reagent DOTAP (N[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium-methylsulfat e). The results provided by these assays were similar. However, the lactate dehydrogenase assay was more sensitive in measuring early damages of cell membranes than the Trypan blue assay. Also, cell morphology showed early toxic changes, such as cytoplasmic vacuolization and cell shrinking, and it should be included with such toxicity evaluations. DDAB:DOPE was more toxic than DOTAP. The cells treated with DOTAP at 10 microM were surviving as well as the control cells, while DOTAP at 40 uM and DDAB:DOPE at 10 microM had slight toxic effects on CaSki cells. The most toxic effects were seen in CaSki cells after treatment with DDAB:DOPE at 40 microM.

Dependence of electroosmotic flow in capillary electrophoresis on Group I and II metal ions

The effect of Group I and II metal ions on electroosmotic flow in capillary electrophoresis in fused-silica capillaries is characterized. The electroosmotic mobility of aqueous mobile phases of lithium, sodium, potassium, calcium and barium acetates in fused-silica capillaries is measured as a function of pH at constant voltage. Cross contamination is avoided by using separate columns for each study and pH control is maintained with the aid of He sparging. The shape of a plot of pH vs. electroosmotic mobility depends on the particular cation used which in turn depends on the surface sorption properties of the ions. Column history is demonstrated to have an effect on electroosmotic flow and therefore retention times. The resolution of a test mixture is optimal in the lithium-based buffer.

Cationic polymers for selectivity control in the capillary electrophoretic separation of inorganic anions

The capillary electrophoretic (CE) separation of the inorganic anions bromide, chloride, nitrate, nitrite, fluoride, sulfate and phosphate is described in 0.005 mol/L sodium chromate electrolyte in the presence of soluble polydisperse ionic polymers (polyelectrolytes). The cationic polyelectrolytes used were as follows: poly(1,1-dimethyl-3,5-dimethylenepiperidinium) chromate, hexadimethrine chromate, poly(1,1-dimethyl-3,5-dimethylenepyrrolidinium) chromate and ((diethylamino)ethyl)-dextran chromate in the concentration range 0.004-0.6% (w/v). These polyelectrolytes were shown to be capable of reversing the direction of the electroosmotic flow as well as inducing changes in analyte electrophoretic mobility, separation selectivity, and resolution. Changes in electrophoretic mobility by as much as 25% were observed for the sulfate anion, and the resolution of fluoride and phosphate was enhanced by a factor of 7.8. In the presence of 0.05-0.17% w/v poly(1,1-dimethyl-3,5-dimethylenepyrrolidinium) chromate at pH 8, separation currents were found to increase only slightly as compared to an electrolyte containing equivalent amounts of sodium chromate. Electroosmotic flow was also found to be fairly constant (+/- 16%) in the pH range 6.55-10.02 for 0.01% (w/v) poly(1,1-dimethyl-3,5-dimethylenepiperidinium) chromate at an ionic strength of 0.04, compared to a 400% change in the absence of the polyelectrolyte. The reproducibility of the electroosmotic mobility was between 0.36 and 6% RSD, and analyte electrophoretic mobility was between 0.01 and 1.6% RSD. Peak height reproducibility was 0.2-8.0% RSD. Separation efficiencies were between 258,000 and 780,000 theoretical plates, and detection limits were between 4.4 x 10(-7) and 9.1 x 10(-6) mol/L.

Interactions between metal ions and poly(ethylene glycol) in the fusion of human erythrocytes

Diffusion of the fluorescent membrane probe, Dil-C16 (3), from labelled to unlabelled human erythrocytes has been employed to monitor hemi-fusion (membrane fusion) in monolayers of cells exposed to poly(ethylene glycol) (PEG). Diffusion of the cytoplasmic probe, 6-carboxyfluorescein, was used similarly to monitor cell fusion (cytoplasmic mixing). Hemi-fusion, which is normally seen when erythrocytes are exposed to dehydrating concentrations of commercial PEG 6000, did not occur when the PEG was pretreated with Chelex 100 resin to remove metal ions. Cytoplasmic mixing, which is normally observed when the dehydrated erythrocytes are substantially rehydrated, also failed to occur when both PEG 6000 and the rehydrating buffer had been treated with Chelex 100. The re-addition to Chelex-treated PEG of components removed by the resin, and the addition of 10 mu mM concentrations of La3+ or Al3+, restored its ability to induce hemi-fusion and cell fusion. Higher concentrations of several other metals, including Ca2+, were also effective. These observations show that metal ions are required for hemi-fusion with erythrocytes in the presence of PEG, and that dehydration alone is insufficient to induce hemi-fusion. Phosphatidylserine was apparently not accessible in erythrocytes treated with PEG 6000 until the cells were rehydrated. This indicates that metal ions do not assist the hemi-fusion of erythrocytes by forming trans complexes with surface phosphatidylserine when the cells are dehydrated by PEG.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody catalyzed cationic cyclization

Two major goals for the design of new catalysts are the facilitation of chemical transformations and control of product outcome. An antibody has been induced that efficiently catalyzes a cationic cyclization in which an acyclic olefinic sulfonate ester substrate is converted almost exclusively (98 percent) to a cyclic alcohol. The key to the catalysis of the reaction and the restriction of the product complexity is the use of antibody binding energy to rigidly enforce a concerted mechanism in accord with the design of the hapten. Thus, the ability to direct binding energy allows the experimenter to dictate a reaction mechanism which is an otherwise difficult task in chemistry. New catalysts for cationic cyclization may be of general use in the formation of carbon-carbon and carbon-heteroatom bonds leading to multi-ring molecules including steroids and heterocyclic compounds.

Effect of the addition of electrolytes on the partition coefficients, activity coefficients, and acid dissociation constants of carnitine and its acetyl and propionyl derivatives

The partition coefficients, P, between n-octanol and water of carnitine, acetylcarnitine, propionylcarnitine, and tetraethylammonium pentacyanopropenides have been determined spectrophotometrically at 20 degrees C. The value of P increases upon addition of electrolytes, the increase produced by LiCl being particularly high. The carnitine cations are 'salted-out' by electrolytes as shown by the variation of their 'single-ion' activity coefficients (relative to that of the tetraethylammonium ion) with electrolyte concentration. These cations are appreciably more hydrated than the reference tetraethylammonium ion. The considered carnitine cations are at least one pKa (where Ka is the acid dissociation constant) unit more acidic than butanoic acid in water at 25 degrees C. Electrolyte addition somewhat increases the pKa of these cationic acids.

An assessment of the effect of the helix dipole in protein structures

The locations of the cations bound to the peptide group at the C-termini and the anions attached to the main-chain NH group at the N-termini of helices are analysed. The ions are hardly found along the helical axis, where the effect due to the helix macrodipole is likely to be the maximum. The disposition of the ions appears to be controlled more by the stereoelectronic requirements of the ligand group rather than any long distance electric field. This and other related structural observations call for some circumspection in assigning a role for the helix dipole in protein structure and function.

Age-related alterations of proteoglycan in mouse tracheal cartilage matrix: an electron histochemical analysis with the cationic dye of polyethyleneimine

Age-related alterations of the proteoglycans (PGs) contents and size were observed in the tracheal cartilage matrix of ddY mice at various ages with the cationic dye of polyethyleneimine (PEI). In young animals (aged 1 day to 1 month after birth), the PGs content and size increased, resulting in the formation of the territorial matrix (TM) and the decrease of the space between the PEI aggregates and the collagen fibers. In 1 month old mice, the TM could be distinguished from the interterritorial matrix (ITM). In adult mice (from 2 to 6 months), the PGs content and size kept stable, but the rearrangement of the PGs and collagen fibers was observed. From 6 months of age on, the decrease of PGs content and size occurred mainly in the ITM. The developing stopping sign was recognized in 1 month and the senile sign from 6 months in the ddY mice as for the complete formation of the TM in 1 month and the decrease of the PGs content and size from 6 months. These results demonstrated the age-related alteration of PGs in the ultrastructural level first and could contribute to the aging study of the tracheal cartilage.

Thallium counterion distribution in cubic insulin crystals determined from anomalous x-ray diffraction data

To determine the distribution of monovalent cations around a protein we have measured anomalous scattering diffraction data from Tl-containing cubic insulin crystals at pH 8 and pH 10.5. The differences between Bijvoet reflection pairs within each set of data were used to calculate anomalous scattering difference maps. Both maps show the same six Tl+ sites, which include two well-ordered Tl+ ions previously identified from isomorphous exchange experiments. The other four sites constitute a second class of cations, which, while much more mobile than the protein atoms, are associated with particular ligating groups. Three of the six Tl+ sites are created exclusively by protein main and side chain carbonyl dipoles rather than negatively charged groups. All of the Tl+ ions are positioned so as to interact with both protein atoms and water molecules. The Tl+ occupancies appear to depend in a complex way on interactions with each other and flexibility in the protein structure. The combined occupancies of these cations are slightly less than is required to neutralize the net protein charge of approximately -2e at pH 8 but account for only about half of the approximately -5e protein charge at pH 10.5. Thus, more disordered counterions, not seen in these Bijvoet anomalous scattering difference maps, are more numerous at higher protein net charge.

Structural roles of calcium ions and side chains in welan: an X-ray study

Welan is the first branched polymer in the gellan family of polysaccharides whose three-dimensional structure has been determined by X-ray diffraction analysis of polycrystalline and well oriented fibers of the calcium salt. The molecule exists as a half-staggered, parallel, double-helix, similar to that of gellan. The side chains fold back on the main chain to form hydrogen bonds with the carboxylate groups. This shielding enhances the stability of the double-helix. Three molecules are organized in a trigonal unit cell of dimensions a = 20.83 and c = 28.69 A with a lateral separation of 12.0 A in each pair; this is 2.9 A larger than in gellan. The double helices are in contact with each other through calcium ions and water molecules via COO-...Ca2+...COO- and COO-...W...Ca2+...COO- interactions, and through side chain-side chain hydrogen bonds. These structural features enable us not only to explain how the side chains in welan are responsible for the enhanced molecular stability relative to gellan, but also to show how essential they are for the associative properties which control the rheology of the polymer.

Control of in vivo fate of albumin derivatives utilizing combined chemical modification

Three types of bovine serum albumin (BSA) derivatives such as lactosylated BSA (LBSA), mannosylated BSA (Man-BSA), and cationized BSA (cBSA) were synthesized and their hepatic disposition characteristics in mice were evaluated by pharmacokinetic analysis. At lower doses (< or = 1 mg/kg), LBSA and Man-BSA were very rapidly eliminated from the blood circulation due to uptake by parenchymal and nonparenchymal cells of the liver, respectively, via receptor-mediated endocytosis (Nishikawa et al., 1992; Nishida et al., 1991a, b). These uptake processes were nonlinear and the apparent hepatic uptake clearances (CLliver) were decreased at administered doses higher than 1 mg/kg, e.g. 10, 20, and 100 mg/kg. The liver accumulation of cBSA was also nonlinear, but its binding and/or uptake capacity in the liver was larger than those of LBSA and Man-BSA; i.e., CLliver decreased at doses higher than 20 mg/kg. In the next step, we modified these BSA derivatives by attaching polyethylene glycol (PEG), a modifier known to reduce the hepatic uptake and increase plasma retention, to achieve precise control of the in vivo disposition characteristics of BSA derivatives. By conjugation with PEG having a molecular weight of 10 kDa, the CLliver values of LBSA, Man-BSA, and cBSA were decreasing to one-seventh, one-fortyfifth, and one-onehundredthirtieth, respectively. However, liver accumulation of PEG modified LBSA and Man-BSA at 24 h after i.v. injection was not significantly different from unmodified BSA derivatives. These results suggest that it is possible to control the hepatic uptake of protein drugs by a combination of introduction of charge or sugar moieties and PEG conjugation.

Equilibrium association constants for oligonucleotide-directed triple helix formation at single DNA sites: linkage to cation valence and concentration

The linkage between the energetics of oligonucleotide-directed triple helix formation and the cationic solution environment has been investigated in mixed-valence salt solutions. Equilibrium constants for formation of the local pyrimidine.purine.pyrimidine structure afforded by binding of the oligonucleotide 5'-d(T*TTTTCTCTCTCTCT)-3' to a single site within a 339-bp plasmid fragment were measured using quantitative affinity cleavage titrations at pH 7.0 and 22 degrees C in the presence of various concentrations of KCl, MgCl2, and spermine tetrahydrochloride (SpmCl4). In a solution containing 10 mM NaCl, 140 mM KCl, 1.0 mM MgCl2, and 1.0 mM SpmCl4, the measured binding constant was 3.3 (+/- 1.4) x 10(5) M-1. The equilibrium constant previously reported for the same association reaction in 100 mM NaCl and 1 mM SpmCl4 at the same temperature and pH was 10-fold higher [Singleton, S. F., & Dervan, P. B. (1992) J. Am. Chem. Soc. 114, 6957-6965]. Further study demonstrated that varying the potassium ion concentration between 5.0 and 140 mM (in the presence of 10 mM NaCl, 1.0 mM MgCl2, and 1.0 mM SpmCl4) resulted in an overall 100-fold decrease in the binding affinity from the lowest to the highest concentration. In contrast, measured binding constants increased 500-fold as the spermine concentration was increased from 0.40 to 4.0 mM (in the presence of 10 mM NaCl, 140 mM KCl, and 1.0 mM MgCl2). There was a modest effect on the binding constant (a 3-fold decrease) upon varying the magnesium ion concentration from 0.10 to 10 mM (in the presence of 10 mM NaCl, 140 mM KCl, and 1.0 mM SpmCl4).(ABSTRACT TRUNCATED AT 250 WORDS)

Reactions of captopril and epicaptopril with transition metal ions and hydroxyl radicals: an EPR spectroscopy study

In the present study, using the technique of EPR spin trapping with DMPO a spin trap, we demonstrated formation of thiyl radicals from thiol-containing angiotensin converting enzyme (ACE) inhibitor captopril (CAP) and from its stereoisomer epicaptopril (EPICAP), a non-ACE inhibitor, in the process of .OH radical scavenging. Splitting constants of DMPO/thiyl radical adducts were identical for both thiols and were aN = 15.3 G, and aH = 16.2 G. Bimolecular rate constants for the reaction of CAP and EPICAP with .OH radicals were close to a diffusion-controlled rate (approximately 2 x 10(10) M-1s-1). Our data also show that both CAP and EPICAP reduce Fe(III) ions and that their respective thiyl radicals are formed in this reaction. In the presence of Fe(III), H2O2, and CAP, or EPICAP, .OH radicals were produced by a thiol-driven Fenton mechanism. Copper(II) ions were also reduced by these thiols, but no thiyl radicals could be detected in these reactions, and no .OH or other Fenton oxidants were observed in the presence of H2O2. Our data show direct evidence that thiol groups of CAP and EPICAP are involved in scavenging of .OH radicals. The direct .OH radical scavenging, together with the reductive "repair" of other sites of .OH radical attack, may contribute to the known protective effect of CAP against ischemia/reperfusion-induced arrhythmias. The formation of reactive thiyl radicals in the reactions of the studied compounds with .OH radicals and with Fe(III) ions may play a role in some of the known adverse effects of CAP.

Fusion of dioleoylphosphatidylcholine vesicles induced by an amphiphilic cationic peptide and oligophosphates at neutral pH

Peptide E5 is an analogue of the fusion peptide of influenza virus hemagglutinin and K5 is a cationic peptide which has an arrangement of electric charges complementary to that of E5. We reported that a stoichiometric mixture of E5 and K5 caused fusion of large unilamellar vesicles (LUV) of neutral phospholipids (Murata, M., Kagiwada, S., Takahashi, S. and Ohnishi, S. (1991) J. Biol. Chem. 266, 14353-14358). K5 caused fusion of LUV composed of dioleoylphosphatidylcholine (DOPC) at pH > 10, but not at neutral pH. In the presence of oligophosphates, such as 1 mM ATP, GTP, or polyphosphate, K5 caused rapid and efficient fusion of DOPC LUV at neutral pH without hydrolysis of oligophosphate groups, but another anions such as citrate, acetate, AMP, phosphate, or EDTA were ineffective. The peptide/oligophosphate-induced fusion behaviors have been investigated by a fluorescence resonance energy transfer assay for lipid mixing of LUV and negative staining electron microscopy. At higher ionic strengths ( > 0.3 M KCl) or in the presence of 5.0 mM MgCl2, the fusion was inhibited. Even at the inhibitory conditions, the association of K5 with lipid vesicles at neutral pH was directly confirmed by the Ficoll gradient assay method and by blue shifts of the tryptophan fluorescence of the peptide. A nonhydrolyzable GTP analogue, GTP gamma S, also induced fusion. These observations suggested that the electrostatic interactions between the positive and negative charges of K5 and oligophosphate, respectively, induced complex formation, triggering membrane fusion.

A mechanism for ion selectivity in potassium channels: computational studies of cation-pi interactions

A combination of computational methods has been used to evaluate the interaction between the pi face of a benzene molecule and the monovalent cations of lithium, sodium, potassium, and rubidium. In the gas phase, the ions are strongly bound, and the affinity for benzene follows the expected electrostatic trend (lithium, largest; rubidium, smallest). However, in an aqueous environment, a reordering occurs such that the potassium ion is preferred over all the other ions for 2:1 benzene:ion complexes. The selectivity sequence parallels that seen in voltage-gated potassium channels. Given that several conserved aromatic residues are present in the pore region of such channels, these results suggest that the cation-pi interaction may be responsible for the ion selectivity in potassium channels.

Molecular dynamics of the methylammonium cation in [CH3NH3]5Bi2Cl11

The 1H relaxation times T1 of methylammonium in chlorobismuthate(III) were measured in the temperature range from 50 to 270 K with a SXP 4/100 Bruker pulse spectrometer at 55.2 MHz. It was found that the T1 temperature dependence has three minima. The individual relaxation rates of the three-proton groups can be described by the O'Reilly and Tsang formula. The results obtained from the fitting procedure, using the typical Woessner formula for complex compounds, allow to conclude that the low-temperature minimum is due to the relaxation of all CH3 groups and the other two minima are due to the relaxation of two and four NH3 groups, respectively. This assignment is based on the X-ray results showing that methylammonium cations are differently bonded in this crystal.