Alcohol induces interdigitated domains in unilamellar phosphatidylcholine bilayers

Using the atomic force microscope (AFM) in situ, we have demonstrated that acyl chain interdigitation can be induced reversibly by alcohol in supported unilamellar phospholipid bilayers. At alcohol concentrations considerably lower than the critical values determined by other experimental techniques, it was found that interdigitated domains can be induced and these domains were stable over a long period of time. The mechanism of such domain formation remains to be elucidated. This work also serves as an example to illustrate the uniqueness of the AFM as a powerful tool in the study of membrane structure and conformation under physiological conditions at high spatial resolution.

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.

Cyclodextrins as mucosal absorption promoters of insulin. II. Effects of beta-cyclodextrin derivatives on alpha-chymotryptic degradation and enteral absorption of insulin in rats

The relative effectiveness of two beta-cyclodextrin derivatives, i.e., dimethyl-beta-cyclodextrin (DM beta CD) and hydroxypropyl-beta-cyclodextrin (HP beta CD), in enhancing enteral absorption of insulin was evaluated in the lower jejunal/upper ileal segments of the rat by means of an in situ closed loop method. The incorporation of 10% (w/v) DM beta CD to a 0.5 mg/ml porcine-zinc insulin solution dramatically increased insulin bioavailability from a negligible value (approximately 0.06%) to 5.63%, when administered enterally at a dose of 20 U/kg. However, addition of 10% (w/v) HP beta CD did not improve enteral insulin uptake significantly with a bioavailability of only 0.07%. Similarly, the pharmacodynamic relative efficacy values obtained after the enteral administration of 20 U/kg insulin, 20 U/kg insulin with 10% HP beta CD, and 20 U/kg insulin with 10% DM beta CD were 0.24%, 0.26%, and 1.75%, respectively. Biodegradation studies of 0.5 mg/ml insulin hexamers by 0.5 microM alpha-chymotrypsin revealed no inhibitory effect on the enzymatic activity by the two cyclodextrins. On the contrary, the apparent first-order rate constant increased significantly in the presence of 10% DM beta CD, suggesting insulin oligomer dissociation by DM beta CD. Histopathological examination of the rat intestine was performed to detect tissue damage following enteral administration of the beta-cyclodextrin derivatives. Light microscopic inspection indicated no observable tissue damage, thereby arguing direct membrane fluidization as the primary mechanism for enhanced insulin uptake. This study indicates the feasibility of using cyclodextrins as mucosal absorption promoters of proteins and peptide drugs.

Sequencing and characterization of the sdaC gene and identification of the sdaCB operon in Escherichia coli K12

We describe here the regulatory and coding region, and DNA sequence, for a newly recognized gene, sdaC, which codes for a hydrophobic protein with several predicted membrane-spanning domains. sdaC and sdaB form a single operon, with 57 bp between the end of sdaC and the start of sdaB. Expression of the sdaCB operon is regulated mainly by catabolite repression, but is also slightly sensitive to regulation by leucine-responsive regulatory protein. Cells carrying sdaC on a multicopy plasmid have increased L-serine transport capacity, insensitive to threonine, suggesting that sdaC might code for a recently described highly specific serine transporter [Kayahara, T., Thelen, P., Ogawa, W., Inaba, K., Tsuda, M., Goldberg, E. B. & Tsuchiya, T. (1992) J. Bacteriol. 174, 7482-7485].

Planar waveguide refractive index distribution functions determined precisely from mode indices

The inverse WKB (IWKB) approximation has been extended to derive the index distribution functions from the measured mode indices of a planar waveguide. Through the use of this technique, the forms of the index distribution functions are obtained by IWKB approximation and a criterion is used to derive the functions accurately. The results are compared to the exponential and Fermi distributions. It is shown that the index profile, surface index, and waveguide depth can be obtained more accurately than with the original IWKB approximation. Finally, the index distribution function of a c-cut proton-exchanged LiTaO(3) waveguide is given by this technique, the mode indices calculated with this function agree with the experimental results in the range of 10(-4).

Photorefractive-crystal shape-parameter influence on formation of self-pumped phase conjugation

The influence of crystal-shape parameters on formation of self-pumped phase conjugation is studied experimentally. The parallelism of two c-cut faces of a barium strontium potassium niobate crystal of cuboid shape is changed to control the internal oscillation and thus to induce or to suppress the generation of self-pumped phase conjugation.

Tris(hydroxymethyl)aminomethane (C4H11NO3) induced a ripple phase in supported unilamellar phospholipid bilayers

A commonly used buffer compound, tris(hydroxymethyl)aminomethane (C4H11NO3), was found to induce a ripple phase in supported unilamellar phospholipid bilayers at room temperature. The ripple structure showed various types of domains that could extend to several micrometers in length with many well-defined bendings of either 120 degrees or 60 degrees. Two different periodic ripples were found to coexist in 1,2-dipentadecanoyl-sn-glycero-3-phosphatidylcholine bilayers. Some intermediate states during the transition to the ripple phase were also observed.

Expression of the retinoic Acid nuclear receptors (rars) and retinoid x-receptor (rxr) genes in estrogen-receptor positive and negative breast-cancer

Retinoid inhibition of breast carcinoma growth correlates with the estrogen receptor (ER) positivity and elevated retinoic acid nuclear receptor (RARalpha) mRNA levels. We therefore examined retinoid nuclear receptor mRNA levels in patient breast carcinoma biopsy specimens to determine if such a correlation exists between ER positivity and RARalpha mRNA levels. We have now shown that RARalpha mRNA levels are significantly higher in ER positive samples. RARgamma mRNA is expressed at relatively high levels in a majority of the tumor samples independent of the ER-status while RARbeta mRNA was expressed at low levels in only one tumor sample. We also found high RXRalpha mRNA levels in all of the tumor samples examined while RXRgamma mRNA could not be detected. Our study demonstrates that RARalpha mRNA levels are either low or absent in ER-negative patient samples and that RARalpha levels may serve as a potential marker to determine patient responsiveness to RA therapy.

Molecular resolution atomic force microscopy of soluble proteins in solution

We introduce a simple specimen preparatory method for atomic force microscopy of soluble proteins in aqueous solutions. It is demonstrated that the mica surface is suitable for direct adsorption of macromolecules that are sufficiently stable to withstand the disturbance of the probe for reproducible imaging at high resolution. It is also shown that the main problem impeding successful imaging is the excessive adsorption of macromolecules, as loosely bound macromolecules readily stick to the tip and produce various imaging artifacts.

Behavior of extraordinary rays in uniaxial crystals

We have experimentally investigated the behavior of extraordinary rays (E rays) in uniaxial crystals for two cases: that in which optical axes are parallel to the surfaces and that in which they are inclined. The E ray always rotates around the ordinary ray (O ray) in the same direction that the crystal rotates around its surface normal. For the case when the axes are parallel to the surface, we discovered that the E ray rotates up to α = 2π as the crystal rotates to ? = π. The E ray traces a series of ellipses as the angle of incidence is varied. Snell's law is valid for the E ray only when the optical axes are perpendicular to the plane of incidence. For the case in which the optical axes are incident, the E ray and the crystal rotate at different speeds except for the case of normal incidence. The speed of rotation increases with the incidence angle. The ray traces a curve known as the Pascal worm, which is described by the equation (x(2) + z(2) - mx)(2) = n(2)(x(2) + z(2)). When the optical axes coincide with the plane of incidence, the space between the rays in the plane is not related to the angle of incidence.

The physicochemical properties, plasma enzymatic hydrolysis, and nasal absorption of acyclovir and its 2'-ester prodrugs

A series of 2'-(O-acyl) derivatives of 9-(2-hydroxyethoxymethyl)guanine (acyclovir) was synthesized by acid anhydride esterification. Aqueous solubilities in isotonic phosphate buffer (pH 7.4), partition coefficients in 1-octanol/phosphate buffer, and hydrolysis kinetics in rat plasma were determined. The ester prodrugs showed consistent increases in lipophilicity with corresponding decreases in aqueous solubility as a function of side-chain length. The bioconversion kinetics of the prodrugs appear to depend on both the apolar and the steric nature of the acyl substituents. When perfused through the rat nasal cavity using the in situ perfusion technique, acyclovir showed no measurable loss from the perfusate. Nasal uptake of acyclovir prodrugs, on the other hand, were moderately improved. Furthermore, the extent of nasal absorption appears to depend on the lipophilicity of the prodrugs in the descending order hexanoate > valerate > pivalate > butyrate. Simultaneous prodrug cleavage by nasal carboxylesterase was also noted in the case of hexanoate.

Bile salt-fatty acid mixed micelles as nasal absorption promoters. III. Effects on nasal transport and enzymatic degradation of acyclovir prodrugs

The absorption enhancement and presystemic degradation kinetics of a homologous series of acyclovir 2'-ester prodrugs were investigated in rats using the in situ nasal perfusion technique in the presence of bile salt-fatty acid mixed micelles. In vitro incubation studies indicated that nasal perfusate containing a mixed micellar solution generated higher ester-cleaving activity than isotonic phosphate buffer washings. Inhibitor screening and substrate specificity studies demonstrated the enzyme to be most likely carboxylesterase rather than true cholinesterase. The extent of prodrug cleavage by the carboxylesterase appears to correlate well with the substrate lipophilicity for esters with linear acyl chains. On the other hand, branching of the acyl side chain significantly retards acyclovir prodrug breakdown. To estimate the nasal epithelial membrane and cytoplasmic damaging effect caused by sodium glycocholate (NaGC)-linoleic acid (15 mM:5 mM) mixed micelles, the release profiles of 5'-nucleotidase (5'-ND), lactate dehydrogenase (LDH), and carboxylesterase in the nasal perfusate were measured as a function of time. The results indicated that the activities of all three enzymes resulting from the mixed micellar solution appeared to be significantly higher than those caused by 15 mM NaGC alone. The apparent nasal absorption rate constants of acyclovir and its butyrate, valerate, pivalate, and hexanoate ester prodrugs in mixed micellar solutions containing an esterase inhibitor (1 mM phenylmethylsulfonyl fluoride) were individually calculated. Without an inhibitor, lengthening of the linear acyl side chain of the prodrug resulted in greatly accelerated degradation coupled with moderate absorption improvement. The solubilities and micellar binding constants of acyclovir prodrugs were also determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and stability of pertussis toxin studied by in situ atomic force microscopy

Pertussis toxin, both complete and the B-oligomer, were imaged by atomic force microscopy (AFM), using specimens prepared by simple surface adsorption on mica without further manipulation. The spatial arrangement of the subunits of the B-oligomer was clearly resolved, representing the first protein quaternary structure obtained by AFM in situ. The results suggest that the B-oligomer is a flat pentamer with the two large subunits located next to each other, and the catalytic A-subunit situated at the center above. We found that the B-pentamer was structurally stable for temperatures up to 60 degrees C and within the pH range of 4.5-9.5. It is also demonstrated that the AFM was capable of resolving features down to 0.5 nm on the B-oligomers, indicating its great potential for structural determination.

Chemical and alpha-chymotrypsin-mediated proteolytic degradation of insulin in bile salt-unsaturated fatty acid mixed micellar systems

The proteolytic degradation of porcine zinc insulin by alpha-chymotrypsin was previously found to depend markedly on the state of insulin aggregation (Pharm. Res. 9:864-869, 1992). In this study, the effect of bile salt-unsaturated fatty acid mixed micelles on alpha-chymotryptic degradation of insulin was further characterized. The incorporation of linoleic acid has greatly accelerated insulin degradation with the apparent first order rate constant being linearly related to the concentration of linoleic acid. At a 10 mM linoleic acid concentration solubilized in 10 mM sodium glycocholate, the proteolytic degradation rate constant increased by 16 times, which could not be explained solely by the mechanism of insulin oligomer dissociation. Further, this effect is significantly reduced when the free carboxylic group of linoleic acid is methylated. The catalytic role of mixed micelles on chemical degradation of insulin was found to depend on the concentration of linoleic acid incorporated. When solubilized in the form of mixed micelles, linoleic acid chemically catalyzes peptide bond cleavage in a concentration-dependent manner.

Effect of probe force on the resolution of atomic force microscopy of DNA

Experimental results are presented to show that the adhesion force is the single most important limiting factor in high-resolution atomic force microscopy of DNA in air, prepared by the cytochrome-C-assisted spreading method. It is also shown that humidity plays a minor role in the control of probe force. Using a pure carbon film as the substrate to clean the AFM tip prior to imaging, it is demonstrated that 4-6 nm resolution on DNA can be routinely obtained by the atomic force microscope with commercial Si3N4 pyramid cantilevers. We also show that in organic solvents a resolution of up to 3 nm can be obtained under optimal conditions.

The dynamics of aging and mortality in the People's Republic of China, 1957-1990

The Strehler-Mildvan modification of the Gompertz relationship between aging and mortality predicts a negative linear relationship between the theoretical logarithm of the mortality rate at birth (log R0) and the exponential rate of increase (alpha) in the age-specific mortality rates under specified conditions. This prediction has been generally validated using mortality data from the United States with respect to general and many disease-specific age-specific mortality rates by the method of longitudinal Gompertzian analysis. Estimated age-specific mortality rates from the People's Republic of China for seven years from 1957 to 1990 were analyzed using the method of longitudinal Gompertzian analysis. The results in this population further validate the Strehler-Mildvan modification of the Gompertz relationship between aging and mortality.

Sequencing and characterization of the sdaB gene from Escherichia coli K-12

The sdaB gene which codes for the second L-serine deaminase (L-SD) of Escherichia coli K-12 has been sequenced and shown to be very similar to the sdaA gene which codes for the first L-serine deaminase. sdaB is transcribed in rich medium, particularly in the absence of glucose, and is under the control of catabolite activator protein. A mutation which established expression of the sdaB gene and synthesis of L-serine deaminase 2 in minimal medium has been demonstrated to result in a change in the ribosome-binding site of the sdaB gene.

Thickness determination of biological thin sections by multiple-least-squares fitting of the carbon K-edge in the electron energy-loss spectrum

We show that the local thickness of biological thin sections can be measured by fitting the electron energy-loss spectrum of the plurally scattered carbon K-edge, and that such measurements are consistent with the results obtained by a conventional method based on the relationship t/lambda alpha ln(It/I0). The new method allows the simultaneous measurement and/or mapping of both local thickness and core-level excitations (e.g. Ca L-edge) in this energy range (280-400 eV) without requiring the measurement of the zero-loss and the valence/plasmon excitations.

Differential effects of anionic, cationic, nonionic, and physiologic surfactants on the dissociation, alpha-chymotryptic degradation, and enteral absorption of insulin hexamers

Various surfactants were investigated to compare their effects on insulin dissociation, alpha-chymotryptic degradation, and rat enteral absorption. With a circular dichroism technique, sodium dodecyl sulfate (SDS) at a 5 mM concentration was found to completely dissociate porcine-zinc insulin hexamers (0.5 mg/ml) into monomers. The catalytic activity of alpha-chymotrypsin (0.5 microM) was also abolished by 5 mM SDS. When insulin was injected into the distal jejunum/proximal ileum segment of the rat, 5 mM SDS greatly enhanced its pharmacological availability, from a negligible value to 2.8%. Being a cationic surfactant, hexadecyl trimethylammonium bromide (CTAB) also efficiently dissociated insulin hexamers at concentrations of 1-5 mM. However, extensive charge-charge interaction was observed below a CTAB concentration of 0.6 mM, leading to insulin precipitation at a molar CTAB:insulin ratio of 1:1 to 2:1. An alpha-chymotryptic degradation study also revealed near-complete dissociation of insulin hexamers at 1 mM CTAB. Above 1 mM, however, CTAB acted as an enzyme inhibitor, most likely by means of charge repulsion. Enteral absorption studies showed a much lower pharmacological availability, only 0.29%. Nonionic surfactants such as Tween 80 and polyoxyethylene 9 lauryl ether were ineffective in dissociating insulin hexamers. Tween 80, at 5 mM, neither significantly altered the alpha-chymotryptic degradation pattern nor enhanced the enteral absorption of insulin. The relative effectiveness of different species of bile salts on insulin hexamer dissociation appeared to be similar. Sodium glycocholate at a 30 mM concentration also significantly increased insulin pharmacological availability, to 2.3%. A morphological study did not reveal any significant alteration of the rat intestinal mucosal integrity after exposure to 5 mM SDS for 30 min.2+ transport.

Pulmonary delivery of free and liposomal insulin

The effects of oligomerization and liposomal entrapment on pulmonary insulin absorption were investigated in rats using an intratracheal instillation method. The results indicated that both dimeric and hexameric insulins can be rapidly absorbed into the systemic circulation, producing a significant hypoglycemic response. Intratracheal instillation of insulin in two different oligomerized states has not resulted in any significant difference in the duration of hypoglycemic effect. However, the initial hypoglycemic response (first 10 min) obtained from intratracheal administration of 25 IU/kg hexameric insulin appears to be slower than that from the 25 IU/kg dimeric insulin, thereby suggesting that hexameric insulin may have a lower permeability coefficient across alveolar epithelium than the dimeric insulin. Intratracheal administration of insulin liposomes (dipalmitoylphosphatidyl choline:cholesterol, 7:2) led to facilitated pulmonary uptake of insulin and enhanced the hypoglycemic effect. Nevertheless, similar insulin uptake and pharmacodynamic response were obtained from both the physical mixture of insulin and blank liposomes and liposomally entrapped insulin.

New approach for atomic force microscopy of membrane proteins. The imaging of cholera toxin

We demonstrate that supported synthetic phospholipid bilayers, which are stabilized by lateral cross-linking in both leaflets, can be used for specimen preparation for atomic force microscopy of purified membrane proteins with high stability and excellent reproducibility under water or low-salt buffer. A bilayer containing 1,2-dipentacosa-10,12-diynoyl-phosphatidylcholine and 20 mol % ganglioside (GM1) was transferred onto the surface of mica from a Langmuir trough. Cholera toxin, both the B-subunit and the complete molecular randomly bound to the gangliosides, were imaged by atomic force microscopy in solution with a resolution of better than 2 nm. The pentameric structure of the B-subunit oligomers was well resolved. This result indicates that, with this preparation procedure, other membrane proteins may be studied at intermediate to high resolution under physiologically relevant conditions without the need for crystallization.

Acyclovir permeation enhancement across intestinal and nasal mucosae by bile salt-acylcarnitine mixed micelles

The purpose of this study was to investigate the absorption enhancement of acyclovir, an antiviral agent, by means of bile salt-acylcarnitine mixed micelles. The specificity, site dependence, palmitoyl-DL-carnitine chloride (PCC) concentration dependence, and effects of absorption promoters on acyclovir absorption via the nasal cavity (N) and four different intestinal segments of the rat, i.e., duodenum (D), upper jejunum (UJ), combined lower jejunum and ileum (LJ), and colon (C) were evaluated. The present study employed the rat in situ nasal and intestinal perfusion techniques and utilized sodium glycocholate (NaGC), three acylcarnitines, and their mixed micelles as potential nasal and intestinal absorption promoters. Acylcarnitines used were DL-octanoylcarnitine chloride (OCC), palmitoyl-DL-carnitine chloride (PCC), and DL-stearoylcarnitine chloride (SCC). All acylcarnitines and NaGC by themselves produced negligible enhancement of acyclovir absorption in the rat intestine, while OCC and SCC were totally ineffective in the nasal cavity. However, the mixed micellar solutions of NaGC with PCC or SCC could significantly increase the mucosal membrane permeability of acyclovir in the colon and nasal cavity. On the other hand, NaGC-OCC mixed micelles slightly increased the absorption of acyclovir by both routes. When a mixed micellar solution of NaGC with PCC was used, the rank order of apparent acyclovir permeability (Papp; cm/sec), corrected for surface area of absorption, was N (10.54 +/- 0.62 x 10(-5)) > D (6.82 +/- 0.30 x 10(-5)) > LJ (2.90 +/- 0.08 x 10(-5)) > C (2.54 +/- 0.14 x 10(-5)) > UJ (2.30 +/- 0.22 x 10(-5)).(ABSTRACT TRUNCATED AT 250 WORDS)

Scanning tunneling microscopy of an ionic crystal: ferritin core

Ferritin molecules were imaged directly in air by scanning tunneling microscopy (STM). The lateral dimensions were close to the values determined by electron microscopy, and the vertical dimension was much reduced. Several clusters of partially naked ferritin cores displayed a hexagonal structure of lattice constant 4.9 +/- 0.5 A. It is thus shown that the STM can be used to image thin ionic crystals at high resolution.