Molecular characterization of a new excitatory insect neurotoxin with an analgesic effect on mice from the scorpion Buthus martensi Karsch

Besides the neurotoxins active on mammals, a new excitatory insect selective toxin with a mice analgesic activity was found and purified from the venom of the scorpion Buthus martensi Karsch (BmK) (Ji, Y.H., Mansuelle, P., Terakawa, S., Kopeyan, C., Yanaihara, N., Hsu, K., Rochat, H., 1996. Toxicon 34, 987; Luo, M.J., Xiong, Y.M., Wang, M., Wang, D.C., Chi, C.W., 1997. Toxicon 35, 723.). This peptide (designated as BmK IT-AP) is composed of 72 amino acid residues. Its primary structure was determined by automated Edman degradation of the N-terminal part of the reduced and S-carboxamidemethylated protein and its lysylendopeptidase degraded fragments. Based on the determined sequence, the gene specific primers were designed and synthesized for 3' and 5' RACE (rapid amplification of cDNA ends). Their partial cDNA fragments obtained by 3' and 5' RACEwere cloned and sequenced and the full length cDNA sequence of BmK IT-AP was then completed by overlapping their two partial cDNA sequences. It encodes a precursor of 90 amino acid residues: a signal peptide of 18 residues and a mature peptide of 72 residues which are consistent with the determined protein sequence of BmK IT-AP. The genomic DNA of the peptide was also amplified by PCR from the scorpion genomic DNA and sequenced, which is a first report on the genomic structure of a scorpion toxin specific for insects. Its sequence revealed an intron of 590 bp inserted in the end part of the signal peptide. The peptide caused a fast excitatory contraction paralysis on house fly larvae. Furthermore, the peptide also showed an obvious analgesic effect on mice, as assayed by using a twisting test model. This effect of BmK IT-AP well characterized at molecular level is first reported among the known scorpion insect neurotoxins.

Solution conformation of brazzein by 1H nuclear magnetic resonance: resonance assignment and secondary structure

Brazzein is a sweet-tasting protein isolated from the fruit of the West African plant Pentadiplandra brazzeana Baillon. It is the smallest and the most water-soluble sweet protein discovered so far, it is also highly thermostable. The proton NMR study of brazzein at 600 MHz (pH 3.5, 300K) is presented. Complete sequence specific assignment of the individual backbone and sidechain proton resonances were achieved using through-bond and through-space connectivities obtained from standard two-dimensional NMR techniques. The secondary structure of brazzein contains one alpha-helix (residues 21-29), one short 3(10)-helix (residues 14-17), two strands of antiparallel beta-sheet (residues 34-39, 44-50) and probably a third strand (residues 5-7) near the N-terminus.

A new antifungal peptide from the seeds of Phytolacca americana: characterization, amino acid sequence and cDNA cloning

An antifungal peptide from seeds of Phytolacca americana, designated PAFP-s, has been isolated. The peptide is highly basic and consists of 38 residues with three disulfide bridges. Its molecular mass of 3929.0 was determined by mass spectrometry. The complete amino acid sequence was obtained from automated Edman degradation, and cDNA cloning was successfully performed by 3'-RACE. The deduced amino acid sequence of a partial cDNA corresponded to the amino acid sequence from chemical sequencing. PAFP-s exhibited a broad spectrum of antifungal activity, and its activities differed among various fungi. PAFP-s displayed no inhibitory activity towards Escherichia coli. PAFP-s shows significant sequence similarities and the same cysteine motif with Mj-AMPs, antimicrobial peptides from seeds of Mirabilis jalapa belonging to the knottin-type antimicrobial peptide.

The cDNA sequence of an excitatory insect selective neurotoxin from the scorpion Buthus martensi Karsch

The full-length cDNA of an excitatory insect selective neurotoxin was amplified from total cDNAs of venomous glands of the scorpion Buthus martensi Karsch (BmK) using the 3'RACE and 5'RACE (rapid amplification of cDNA ends, RACE) method and sequenced. The cDNA encoded a precursor of the insect toxin of 88 amino acid residues, including a signal peptide of 18 residues and a mature toxin of 70 residues. The cDNA deduced sequence of this toxin was homologous with the determined amino acid sequence of BmK IT1, an excitatory insect toxin purified from the scorpion venom, except for three different residues, two at the positions 24-25, and another in the COOH-terminus of the toxin. Among them the COO-terminal residue Gly in the cDNA deduced sequence was predominantly different from the conserved residue Asn found in other known scorpion excitatory insect toxins.

A New Rosmarinic Acid Derivative from Isodon oresbius

Phytochemical reinvestigation of ISODON ORESBIUS afforded, in addition to oleanolic acid, ursolic acid, sodoponin, astragalin, and quercetin-3- O-glucoside, three known (oresbiusin A, rosmarinic acid and methyl rosmarinate) and a new rosmarinic acid derivative as well as an ENT-kaurene diterpenoid, neo-angustifolin, characterized as a separated component for the first time. By a combination of 1D- and 2D-NMR techniques the structure of the new compound was established as butyl rosmarinate. The IN VITRO antifungal assay showed that neoangustifolin was active against CANDIDA ALBICANS with the MIC being 50 microg/ml.

A series of bioactivity-variant neurotoxins from scorpion Buthus martensii Karsch: purification, crystallization and crystallographic analysis

Three bioactivity-variant neurotoxins, BmK M1, M4 and M8, have been purified from Chinese scorpion BmK venom. They possess distinct toxic activities against mice in vivo. These proteins also have different electrostatic properties. The relative toxicities for BmK M1, M4 and M8 are 13.3:2.5:1 which, surprisingly, correspond to their respective pI values ranging from basic to acidic 9.01, 7.53 and 5.30, respectively. They have been crystallized in different crystal forms as orthorhombic, hexagonal and monoclinic, respectively. These crystals can diffract to 1.2 (BmK M1), 1.3 (BmK M4) and 1.8 A (BmK M8) resolution and have been used in data collection. These toxins produced by natural mutagenesis or gene divergence should represent functionally distinct states, thereby forming a valuable system for studying structure-function relationships. The unusual relatively acidic component that first appeared in this series also provides a new concept for a more comprehensive understanding of scorpion neurotoxins.

Internet Technology in Magnetic Resonance: A Common Gateway Interface Program for the World-Wide Web NMR Spectrometer

A custom-written Common Gateway Interface (CGI) program for remote control of an NMR spectrometer using a World Wide Web browser has been described. The program, running on a UNIX workstation, uses multiple processes to handle concurrent tasks of interacting with the user and with the spectrometer. The program's parent process communicates with the browser and sends out commands to the spectrometer; the child process is mainly responsible for data acquisition. Communication between the processes is via the shared memory mechanism. The WWW pages that have been developed for the system make use of the frames feature of web browsers. The CGI program provides an intuitive user interface to the NMR spectrometer, making, in effect, a complex system an easy-to-use Web appliance. Copyright 1998 Academic Press.

Engineering subtilisin YaB: restriction of substrate specificity by the substitution of Gly124 and Gly151 with Ala

The 3-D structure of subtilisin YaB was computer modelled using the structures of subtilisin BPN', subtilisin Carlsberg and thermitase as templates. Gly124 and Gly151 located on both sides of the waist of the S1 pocket were selected for site-directed mutagenesis based on the modelled structure. The mutated ale genes coding for the mutant subtilisin YaB were expressed in Bacillus subtilis DB104. All of the G124 and G151 series of mutants exhibited an increase of relative catalytic activity for elastin-orcein against casein and myofibrillar proteins. The S1 substrate specificity of G124A, G124V and G151A mutants were assessed using various carbobenzoxy-amino acid-nitrophenyl esters and succinyl-Ala-Ala-(Pro or Val)-(Ala, Phe or Leu)-p-nitroanilide [AA(P/V) (A/F/L)]. While G124A and G124V mutants hydrolyzed only Ala and Gly esters, G151A mutant hydrolyzed Ala, Leu and Gly esters. The G124A and G124V mutants did not hydrolyze AAPF and AAPL. However, these two mutants hydrolyzed AAPA and AAVA with kcat/Km values approximately 3-10-fold higher than those of the wild-type enzyme. The G151A mutant did not hydrolyze AAPF, but hydrolyzed AAPL, AAPA and AAVA with kcat/Km values approximately 1-4-fold higher than those of the wild-type enzyme. These results clearly indicate that the S1 substrate specificity of G124A and G124V mutants was restricted to Ala and Gly, and G151A mutant to Ala, Gly and Leu.

Crystallization and preliminary crystallographic analyses of pokeweed antiviral protein from seeds

Pokeweed antiviral protein from seeds (PAP-S) is a ribosome inactivating protein which has lowest toxicity and highest inhibition activity as opposed to other pokeweed antiviral proteins and its three potential glycosylation sites (10, 44, 255) were shown to bind to N-acetylglucosamine. Good quality crystals of PAP-S were grown at high protein concentration (100 mg ml-1) and high temperature (306 K). The crystals have space group I222 and cell parameters a = 78.7, b = 85.2 and c = 93.0 A. An X-ray diffraction data set with resolution up to 1.8 A was collected. This high-resolution data will help to locate the sugars bound to the protein and provide accurate structural data for understanding structure-function relationships of PAP-S.

The CDNA and genomic DNA sequences of a mammalian neurotoxin from the scorpion Buthus martensii Karsch

The cDNA library of venomous glands of the scorpion Buthus martensii Karsch (BmK) was constructed. A cDNA encoding a mammalian neurotoxin corresponding to the known alpha-type toxin, BmK M1, was amplified by polymerase chain reaction (PCR) and cloned, and its full-length sequence was determined. The open reading frame encoded the precursor of BmK M1 with 84 amino acid residues, including a signal peptide of 19 residues, a mature toxin of 64 residues and an additional C-terminal residue Arg which might be cleaved off by proteinase postprocessing immediately after protein synthesis. Based on the determined cDNA sequence and using the total DNA of the scorpion as a template, the gene of BmK M1 was also amplified by PCR and sequenced. The genomic DNA sequence revealed an intron of 408 base pairs present within the signal peptide region. Both the intron and exon of BmK M1 share about 75% similarity with those of AaH I' another alpha-type mammalian neurotoxin in the scorpion Androctonus australis Hector.

Inhibitory effects of copper-aspirin complex on platelet aggregation

AIM

To study the inhibitory effects of copper-aspirin complex (CuAsp) on platelet aggregation.

METHODS

With adenosine diphosphate the effects of CuAsp on platelet aggregation in vitro or in vivo were investigated. Radioimmunoassay and fluorophotometry were used to measure thromboxane B2 (TXB2) generation from platelets, the levels of TXB2 and of 6-keto-PGF1 alpha in plasma and the platelet serotonin release reaction.

RESULTS

In vitro, CuAsp inhibited arachidonic acid (AA)-induced aggregation (IC50 = 17 mumol.L-1, 95% confidence limits: 9-33 mumol.L-1), the release of 5-HT (IC50 = 19 mumol.L-1, 95% confidence limits: 10-30 mumol.L-1), and TXB2 generation from platelets (P < 0.05). CuAsp 10 mg.kg-1 i.g. selectively inhibited AA-induced aggregation, and increased the 6-keto-PGF1 alpha concentration in plasma while decreased that of TXB2.

CONCLUSION

CuAsp, in vitro or in vivo, shows more potent inhibitory effects on AA-induced aggregation than aspirin (Asp), related to the inhibition of platelet cyclooxygenase and the release of active substances from platelets.

Purification and sequence determination of a new neutral mammalian neurotoxin from the scorpion Buthus martensii Karsch

A new neutral mammalian neurotoxin, designated BmK M4, with an isoelectric point (pI) of 7.6 and a relatively low toxicity (LD50 = 4.0 +/- 0.25 microgram/g mice, i.v.) was purified from the venom of scorpion Buthus martensii Karsch (BmK). The complete amino acid sequence of the toxin composed of 64 amino acid residues was determined by automated Edman degradation of the N-terminal part of the reduced and S-carboxamidomethylated protein (up to 30 amino acid residues) and its peptide fragments degraded by lysylendopeptidase or Staphylococcus aureus Va protease. The calculated mol. wt based on the amino acid composition was 7001. By comparison with the sequences of other basic BmK mammalian neurotoxins, it was concluded that the weaker toxicity and lower pI value of BmK M4 might be the result of mutations H10E, R18G and K28D. The sequence comparison of BmK M4 with an acidic toxin, BmK M8, showed that the weakest toxicity and acidic property of BmK M8 may be the consequence of mutations K8D, D53A, V55E and V59E. The substitution of 21 Gly in BmK M4 for Tyrin other BmK toxins may also be of importance. In their tertiary structures, these mutated charged residues are mainly distributed in the surface (face B) that is roughly opposite to the "conserved hydrophobic surface" (face A) proposed by Fontecilla-Camps et al. in 1982. Therefore the toxin-receptor interaction may take a multiposition mode.

Biliary venous fistula from umbilical catheter placement

A case of umbilical venous catheter placement in a premature neonate which resulted in iatrogenic formation of a venous-biliary fistula is presented. A review of pertinent anatomy and appropriate placement parameters for umbilical venous and arterial catheters is included.

Optimization of Transverse Gradient Coils with Coaxial Return Paths by Simulated Annealing

Coils with coaxial return paths are used to generate transverse magnetic field gradients. This paper describes optimization of such coils by the method of simulated annealing, a method known to be able to find the global minimum of a function. The adaptive simulated annealing (ASA) program has been analyzed and applied to optimization of a family of coils with 8-16 building blocks, each carrying equal current. Positions of the blocks along the longitudinal axis of the coils were optimized. A new subclass of coils is proposed; the diameter of return paths of this subclass of coils is not fixed but may be varied. The new coils provide greater gradient uniformity than those for which only positions of the blocks are optimized. All optimized coils should find applications in high-precision and high-resolution imaging and spectroscopic experiments.

Crystal structure of an acidic neurotoxin from scorpion Buthus martensii Karsch at 1.85 A resolution

The crystal structure of an acidic scorpion neurotoxin, BmK M8, purified from Chinese scorpion Buthus martensii Karsch (BmK), has been determined by the molecular replacement method. It is the first structure of an acidic alpha-scorpion neurotoxin reported so far. The crystals adopt a symmetry of space group P2(1) and contain one molecule per asymmetric unit. The structure has been refined to an R factor of 18.1% using reflection data in the range of 8 to 1.85 A resolution, with standard deviations from ideal geometry of 0.017 A and 2.43 degrees for bond length and angle, respectively. The 12 residues at the C terminus with unknown sequence were determined by crystallographic refinement. The refined model shows that the structural core, consisting of a motif beta alpha beta beta, is similar to that of toxin II from Androctonus australis Hector (AaH II) or Variant 3 from Centruroides sculpturatus Ewing (CsE V3). The three conformationally variable loops protruding from this structural core are different from that of AaH II, and especially from that of CsE V3. Compared with the most potent and basic alpha-toxin AaH II, the BmK M8 is a relatively inactive toxin (1100 times less active than AaH II) with an unusually low isoelectric point (pI 5.3). Sequence alignment of the two toxins shows a difference of 26 residues (40.6%). Among them four basic or neutral residues in AaH II, namely Val10, Lys28, Val55 and Gly59, are changed to acidic glutamate in BmK M8. The residues Glu10, Glu28 and Glu55 of BmK M8 are located on a surface (Face B), opposite the "conserved hydrophobic surface" (Face A). The latter is a functionally important area proposed by Fontecilla-Camps et al. Our observations suggest that in addition to Face A, Face B may also be involved in the biological activity of scorpion toxins. The structure of BmK M8 shows an evident conformational change of the alpha-amino group at the N terminus and a deorganization of Arg2 caused by the mutation D53A. These structural changes may also be responsible for the weak toxicity of BmK M8. In association with the information from chemical modifications, a multisite binding mode for toxin-receptor interaction and three "toxic regions" in relevance to the binding process, including Face A, Face B and Site C, are proposed. Face A, mainly consisting of Tyr5, 35, 47, the alpha-amino group, Arg2 and Asp3, may be more essential for the binding. Face B, mainly comprising conserved residues Tyr14, 21, Lys28 and Val55, may contribute to the high efficacy of the binding process and substitutions by acidic residues in this area could strongly weaken the toxic activity. Site C, formed by Lys58 and Arg62 at the C terminus and Arg41 and Tyr42 from loop 38-44, may be involved in binding site specificity.

Abrogation of the Fc gamma receptor IIA-mediated phagocytic signal by stem-loop Syk antisense oligonucleotides

The role of Syk kinase in Fc gamma receptor (Fc gamma R) IIA-mediated phagocytosis was examined with two forms of antisense oligodeoxynucleotides (ODNs) designed to hybridize to human Syk mRNA. Monocytes were incubated with linear and stem-loop antisense ODNs targeted to Syk mRNA. When complexed with cationic liposomes, stem-loop Syk antisense ODN with phosphorothioate modification exhibited stability in fetal bovine and human serum. The stem-loop Syk antisense ODN at a concentration of 0.2 microM inhibited Fc gamma RIIA-mediated phagocytosis by 90% and completely eliminated Syk mRNA and protein in monocytes, whereas scrambled-control ODNs had no effect. The Syk antisense ODNs did not change beta-actin mRNA levels and Fc gamma RII cell-surface expression. In addition, stem-loop Syk antisense ODN inhibited Fc gamma RI and Fc gamma RIIIA-mediated phagocytosis. These data indicate the efficacy of stem-loop Syk antisense ODN for targeting and degrading Syk mRNA and protein and the importance of Syk kinase in Fc gamma receptor-mediated phagocytosis. Immunoblotting assay demonstrated that Fc gamma RII tyrosine phosphorylation after Fc gamma RII cross-linking did not change in the absence of Syk protein. These results indicate that Syk kinase is required for Fc gamma RIIA-mediated phagocytic signaling and that Fc gamma RII cross-linking leads to tyrosine phosphorylation of Fc gamma RII independent of Syk kinase.

Clustered syk tyrosine kinase domains trigger phagocytosis

Phagocytosis is a phylogenetically primitive mechanism adapted by specialized cells of the immune system to ingest particulate pathogens. Recent evidence suggests that the program of specific cytoskeletal rearrangements that underlies phagocytosis may share elements with the antigen receptor signaling pathway in lymphocytes. Tyrosine phosphorylation, necessary for both lymphocyte effector function and phagocytosis, is thought to allow cytoskeletal elements to couple to the intracellular domains of antigen and Fc receptor subunits. We show here that the intracellular domains of the receptors are not inherently required for cytoskeletal coupling. Chimeric transmembrane proteins bearing syk but not src family tyrosine kinase domains are capable of autonomously triggering phagocytosis and redistribution of filamentous actin in COS cells. These responses cannot be initiated by a receptor chimera bearing a point mutation in the syk catalytic domain, and the kinase domain alone is sufficient for initiating cytoskeletal coupling.

[The prevalence of Toxoplasma infection among pregnant women and their newborn infants in Chengdu]

Purpose of the study was to determine the prevalence of toxoplasma infection among the pregnant women and their newborn infants in Chengdu and to identify risk factors of acquiring toxoplasma infection. The Maternal and Child Health Hospital was selected by random cluster sampling method in the study. Each pregnant women admitted to the above hospital consecutively and her surviving newborn at birth were included in this survey. History, physical examination and blood specimens were obtained from 1,211 pairs of mother-newborns. ELISA was used to detect toxoplasma IgG and IgM antibodies. Results revealed that sera prevalence of toxoplasma IgG antibodies and IgM antibodies of pregnant women were 39.14% and 4.21% respectively. Seraprevalence of toxoplasma IgM antibodies of newborn infants was 1.07%. Congenital malformation of newborn infants may be associated with congenital toxoplasma infection (P < 0.05, OR = 6.32).

[Experimental study on the pharmacologic effects of zeng sheng pin pian]

Zeng Sheng Pin Pian (ZSPP) is a mixture of medicinal herbs which has been shown to be effective in the secondary prevention of esophageal cancer in a high-risk area among a population with severe esophageal dysplasia. This study in mice aimed at elucidating the possible mechanism of the cancer-preventing activity of ZSPP. The results indicate that ZSPP is a good biologic response modifier (BRM) as shown by its enhancing effects on lymphocyte blastogenesis, IL-2 secretion, NK cell activity, delayed-type hypersensitivity reaction to DNCB, hemolysin response to SRBC and the phagocytic function of the reticulo-endothelial system. While ZSPP did not inhibit the growth of S-180 in mice, it exhibited significant inhibitory effect on ornithine decarboxylase (ODC) activity induced by the application of croton oil to the skin. Taken together, the immune enhancing activity and the anti-tumor-promoting activity of ZSPP could explain, at least in part, its efficacy in the prevention of esophageal cancer among high-risk people with precursor dysplastic lesions.

Studies on long-acting insulin: crystal structure of Arg-B31 human insulin at 2.0A resolution

The crystal structure of Arg-B31 human insulin (ABHI), a long-acting insulin derivative, has been determined at 2.0 A resolution by using X-ray diffraction analysis. The final crystallographic R factor of the structure model after the refinement is 0.189 with the bond length r. m. s deviation of 0.018 A. The refined structure of ABHI showed that the conformation of B-chain C-terminal residues was more stable than that in the native molecule. A striking structural feature of ABHI was an additional ion pair formed between Arg-B31 of molecule I and Glu-B21 of molecule II in a dimer, and three ionic bonds between the neighbouring molecules thereby appeared on the surface of ABHI hexamer. These secondary bonds generated by the insertion of the residue Arg-B31 should make the rate of dissociation of ABHI hexamer slow down when it was injected into the body and the property of protraction should be produced by a 'depot effect'. This ought to be the main structure basis of the prolonged action of ABHI. The results observed here demonstrate that the main idea we used in search for long-acting insulin is reasonable and correct which goes like this: making some additional non-covalent bonds between insulin monomers so as to slow down the dissociation of insulin oligomers and gain the protraction from a 'depot effect', which may be used as a principle in the further research. It also shows an impressive example that the experimental result reported here is in agreement with the theoretical prediction before the structural determination.

Recurrent conduction in accessory pathway and possible new arrhythmias after radiofrequency catheter ablation

Radiofrequency catheter ablation was performed in 142 patients with 166 accessory pathways. One hundred thirty-six patients with 160 accessory pathways underwent successful ablation in the first ablation session. Serial follow-up electrophysiologic studies were performed immediately (30 minutes), early (5 to 7 days), and late (3 to 6 months) after successful ablation to determine the recurrent accessory pathway conduction and possible new arrhythmias. After a minimum follow-up period of 6 months (mean, 14 +/- 3 months), accessory pathway conduction recurred in 13 patients (9.6%), with recurrent tachycardia in three patients (2.2%). Five of the recurrent accessory pathways had decremental conduction properties. Incidence of recurrent accessory pathway conduction was similar in different accessory pathway locations (6.4% to 9.0%). Patients with concealed accessory pathways (12.2 vs 2.9%; p < 0.05), and patients without accessory pathway potentials in the ablation site (15.5% vs 2.2%; p < 0.05) had a higher recurrence rate. Patients without tachycardia in the late electrophysiologic study did not have recurrent tachycardia during follow-up. New arrhythmias, including atrial and ventricular arrhythmias, which were detected by 24-hour Holter monitoring, were apparent only on the first day after ablation. The findings indicate that the overall incidence of recurrent accessory pathway conduction was low and that possible new arrhythmias were rare in the late follow-up period.

Arrhythmogenicity of catheter ablation in supraventricular tachycardia

To evaluate arrhythmogenicity in patients who receive a modified direct-current (DC) shock ablation (distal pair of electrodes connected in common as the cathode) or radiofrequency (RF) ablation of supraventricular tachycardia, a prospective study was performed with signal-averaged ECG, 24-hour Holter monitoring, electrophysiologic study (EPS) for ventricular tachycardia (VT), and treadmill exercise test. Sixty-nine consecutive patients with documented paroxysmal supraventricular tachycardia were included. Twenty-eight patients proved to have atrioventricular nodal reentrant tachycardia, and 41 patients had atrioventricular reciprocating tachycardia that involved accessory atrioventricular pathways. The first 34 patients received DC shock ablation and the other 35 patients received RF ablation. Signal-averaged ECG, Holter monitoring, and EPS for VT were performed before ablation, immediately after ablation, then 1 week, 2 weeks (Holter monitoring), 1 month (except EPS), and 3 months after ablation. Treadmill exercise testing was performed before ablation, and at 1 week and 3 months after ablation. The root mean square, low-amplitude signal and QRS duration of signal-averaged ECG disclosed no significant change after either DC or RF ablation up to 3 months. Late potential developed in only one patient in the DC shock group and it was considered to be innocuous because neither VT nor ventricular fibrillation was noted or induced. Increases in the number of ventricular premature contractions and in short-run VT were detected by Holter monitoring in the first week after either mode of ablation (p < 0.001 for the DC shock group; p < 0.05 for the RF group), which were greater (p < 0.05) and lasted longer in the DC shock group than in the RF group.(ABSTRACT TRUNCATED AT 250 WORDS)

Configurational entropy is the driving force of ethanol action on membrane architecture

A colligative thermodynamic framework is developed to describe the action of ethanol on membranes. The partitioning of ethanol into a membrane structure imparts a randomness, configurational entropy, that stabilizes that structure from an energetic standpoint. When partitioning between membrane structures differs, the equilibrium between them is altered to favor the structure with the largest partition coefficient for ethanol. The action of ethanol and temperature originate in entropy and are equated through entropy. Membrane equilibria that are predicted to be most sensitive to the action of ethanol (where dilute concentrations of ethanol cause a perturbation equal to a large change in temperature) are those that exhibit a small thermal entropy change and a large difference in solute partitioning between membrane structures. Our model predicts that ethanol does not act on a single membrane structure, but on both structures in an equilibrium. The thermodynamic framework is applied to the action of ethanol on cooperative equilibria in a dipalmitoyl lecithin model membrane. Ethanol-induced perturbations are monitored by electron paramagnetic resonance (EPR) using the spin label, Tempo. The equilibrium between the gel and ripple-structures (L beta'-->P beta', pretransition) exhibits a small change in thermal entropy and, as predicted, is more sensitive to the action of ethanol than the equilibrium between the ripple and fluid bilayer-structures (P beta'-->L alpha, main transition) which exhibits a large thermal entropy change. The framework suggests that ethanol acts through entropy, as does temperature, thereby upsetting the natural thermal balance that maintains membrane architecture.