In vitro studies on a new method for islet microencapsulation using a thermoreversible gelation polymer, N-isopropylacrylamide-based copolymer

Various materials for the semipermeable membrane for microencapsulation of islets, such as alginate complex and agarose, have been used. In this study, a thermoreversible gelation polymer, N-isopropylacrylamide based copolymer was used to make microencapsulated islets and was examined in vitro. The polymer has little or no cytotoxicity for human dermal fibroblasts. The characteristics of viscoelasticity below the soluble gel transition temperature (SGTT) and of thermoreversibility, the water soluble polymer below the SGTT (22 degrees C) becoming water insoluble upon heating, contributed to simplifying the encapsulation technique. We obtained viable islets at the center of the membrane with a thickness of approximately 20-50 microns, accounting for a 40% yield of encapsulated islets. Static glucose challenge test with microencapsulated islets revealed the insulin response to the concentration of glucose. The insulin concentrations of the culture medium in the microencapsulated islet group were the same as those in a similar free islet group up to 42 days. These results indicate that the morphological and functional stability of the new method for microencapsulation may be sufficient for it to be used for transplantation in diabetic animals.

Environmental degradation of polyacrylamides. 1. Effects of artificial environmental conditions: temperature, light, and pH

A polyacrylamide thickening agent (PATA) was formulated at four concentrations in distilled-deionized water, without and with a glyphosate-surfactant herbicide (GH). Over a 6-week period, these mixtures were exposed to various controlled temperature and light conditions. Acrylamide concentration, ammonium concentration, and pH were measured at weekly intervals to assess the degradation of polyacrylamide and acrylamide. Satellite studies were conducted to examine the effect of altered pH on solutions of PATA (i.e., does pH promote polyacrylamide depolymerization?) and GH binding to amine groups (i.e., protection from degradation). The results of these studies suggest that polyacrylamide can degrade to acrylamide by thermal and photolytic effects, that changes in pH do not promote the depolymerization of polyacrylamide, and that GH does protect polyacrylamide and acrylamide from environmental degradation. Statistically there was no linear correlation between the various parameters measured.

Large-pore polydimethylacrylamide resin for solid-phase peptide synthesis: applications in Fmoc chemistry

We have synthesized a hydrophilic crosslinked aminoalkyl polydimethylacrylamide-beaded support upon which peptides have been assembled using standard Fmoc chemistry in automated batch-wise equipment. The resin was prepared by the free radical-initiated co-polymerization of N,N-dimethylacryl-amide, N,N'-bisacrylyl-1,3-diaminopropane and a functional monomer N-methacrylyl-1,3-diaminopropane hydrochlorid. After coupling of N-alpha-tert-butyloxycarbonyl-glycine (Boc-glycine), amino acid analyses gave resin loading capacities of 0.66 mmol/g. The resulting polymer was highly swollen by polar solvents including aqueous buffers and had an exclusion limit of 50 kDa for soluble proteins. This resin was found to be an excellent support for peptide synthesis using Fmoc chemistry. Typical purities of crude peptides were 80%-95%, including sequences that failed on conventional polystyrene resins.

Biocompatibility of sulphonated polyurethane surfaces

Surfaces of medical devices made of polymeric materials may promote thrombosis and inflammation. Therefore, in an attempt to produce surfaces which might diminish biomaterial-mediated thrombosis and inflammation, surface derivatization with 2-acrylamido-2-methylpropanesulphonic acid (AMPS) was carried out. The derivatization procedure generates free radicals which initiate the copolymerization of AMPS monomers directly to a polyurethane surface. In an in vitro blood loop study using non-anticoagulated human blood, the resulting AMPS-derivatized material completely abrogates the generation of fibrinopeptide A, decreases the production of beta-thromboglobulin and C3a, and decreases the adherence of platelets. The derivatized material also attracts fewer adherent neutrophils when implanted in mice. However, AMPS derivatization unexpectedly increases the recruitment of macrophages to implanted material and promotes the formation of adherent sleeve thrombi on central venous catheters indwelling in non-anticoagulated canine femoral veins. Thus, AMPS derivatization has highly variable effects on inflammatory and thrombotic systems. Further investigation is clearly required to determine the mechanisms underlying both desired and adverse effects.

Examination of capillary zone electrophoresis, capillary isoelectric focusing and sodium dodecyl sulfate capillary electrophoresis for the analysis of recombinant tissue plasminogen activator

The microscale techniques of CZE, cIEF and SDS capillary electrophoresis have been evaluated for the analysis of a complex glycoprotein, recombinant tissue plasminogen activator (rtPA). A series of omega-amino acid buffers (pH approximately 5) was found suitable for the CZE separation of rtPA on coated capillaries. rtPA could be resolved into a series of major and minor peaks in an epsilon-aminocaproic acid buffer containing 0.01% (v/v) Tween 80. For cIEF, a two step method with pressure mobilization was utilized. Using a commercial instrument, either a polymer solution with a 50 microns I.D. capillary or narrow bore capillaries without a polymer solution (25 microns I.D.) were employed. rtPA was resolved into at least eight species within a pI range of 6.4-9.2 using Ampholine 3.5-10. Migration time precision for the major peaks ranged from 0.2% for CZE to < or = 2-3% R.S.D. for cIEF. Total recovery of rtPA from the capillary was also demonstrated for both methods. Analysis of rtPA, rtPA Type I, rtPA Type II and the desialylated forms resulted in the expected elution profiles. Finally, the potential of SDS capillary electrophoresis using a coated capillary for an rtPA Type I/Type II purity assay was shown.

Preparation of conjugates between oligonucleotides and N-vinylpyrrolidone/N-acryloxysuccinimide copolymers and applications in nucleic acid assays to improve sensitivity

A simple approach has been developed to prepare conjugates between oligodeoxyribonucleotides (ODNs) and linear copolymers of N-vinylpyrrolidone (NVP)/N-acryloxysuccinimide (NAS). These conjugates were of higher than expected molecular weight, as determined by light scattering. Side reactions between amino groups on heterocyclic bases, especially of cytosine, are proposed to explain the formation of aggregates. ODN-NVP/NAS conjugates used in both capture and detection steps in sandwich hybridization increased assay sensitivity. Sensitivity to 10(7) DNA molecules/mL was reached for a 2.3 kb PCR fragment of hepatitis B virus (HBV) genomic DNA.

Study of protein binding to a silica support with a polymeric cation-exchange coating

A silica-based, polyacrylate ion-exchange stationary phase has been prepared using Ce(IV) as the initiator. Analysis of the physical properties of the polymeric layer separated from the silica surface indicates that the polymeric coating is cross linked to some extent. The polymerization carried out at different concentrations of Ce(IV) demonstrated that the effective surface area can be increased by lowering the Ce(IV) concentration at higher monomer concentrations of the reaction mixture. These materials are quite reproducible and of high electrostatic binding capacity; 1.485 mumol/m2. The electrostatic binding capacity of a non-polymeric stationary phase reached the theoretical limit for a monolayer (0.16 mumol/m2). However, the covalent binding capacity of the same stationary phase was only 50% of the electrostatic binding capacity. The same trend was observed in all the polymeric stationary phases tested. This shows that the mechanism of protein binding in polymeric and conventional stationary phases is similar, and multilayer electrostatic binding is highly unlikely in these sorbents examined. Z numbers revealed that the contact area of the protein is independent of the polymeric character of the stationary phase and therefore, the increased loading of these polymeric stationary phases is due to the increased surface area.

Regioselective immobilization of short oligonucleotides to acrylic copolymer gels

Four types of polyacrylamide or polydimethyl-acrylamide gels for regioselective (by immobilization at the 3' end) of short oligonucleotides have been designed for use in manufacturing oligonucleotide microchips. Two of these supports contain amino or aldehyde groups in the gel, allowing coupling with oligonucleotides bearing aldehyde or amino groups, respectively, in the presence of a reducing agent. The aldehyde gel support showed a higher immobilization efficiency relative to the amino gel. Of all reducing agents tested, the best results were obtained with a pyridine-borane complex. The other supports are based on an acrylamide gel activated with glutaraldehyde or a hydroxyalkyl-functionalized gel treated with mesyl chloride. The use of dimethylacrylamide instead of acrylamide allows subsequent gel modifications in organic solvents. All the immobilization methods are easy and simple to perform, give high and reproducible yields, allow long durations of storage of the activated support, and provide high stability of attachment and low non-specific binding. Although these gel supports have been developed for preparing oligonucleotide microchips, they may be used for other purposes as well.

Accessibility and environment probing using cysteine residues introduced along the putative transmembrane domain of the major coat protein of bacteriophage M13

The major coat protein of the filamentous bacteriophage M13 is located in the inner membrane of host cell Escherichia coli prior to assembly into virions. To identify the transmembrane domain of the coat protein, we have introduced unique cysteine residues along the putative transmembrane domain at position 25, 31, 33, 36, 38, 46, 47, 49, or 50. The mutant major coat protein was solubilized by membrane-mimicking detergents or reconstituted into mixed bilayers of phospholipids. Information about the environmental polarity was deduced from the wavelength of maximum emission, using N-[[(iodoacetyl)-amino)ethyl]-1-sulfonaphthylamine (IAEDANS) attached to the SH groups of the cysteines as a fluorescent probe. Additional information was obtained by determining the accessibility of AEDANS for the fluorescence quencher molecules acrylamide and 5-doxylstearic acid, and the reactivity of the cysteine's sulfhydryl group toward 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). Our data suggest transmembrane boundaries close to residue 25 and 46, with residue 25 inside the hydrophobic part of the membrane in very close proximity to the membrane-water interface and residue 46 located at the membrane-water interface. Domains of the mutant coat protein which are packed or coated by cholate molecules and various other detergents [except for sodium dodecyl sulfate (SDS)] are at least similarly packed by phospholipid molecules in bilayers. SDS is a good solubilizing detergent but badly mimics the typical nature of a membrane structure. The overall results are interpreted with respect to the established conformation of the coat protein and its membrane anchoring mechanism.

Protein electrophoresis in polyacrylamide gels with templated pores

An approach is described for the synthesis of nanostructured hydrogels with defined size channels or pores for separations of biological macromolecules. Polyacrylamide gels (15-20% acrylamide) were cast in the presence of high concentrations (5%-28%) of hydrophilic, macromolecular cosolutes either semirigid, rod-like polyelectrolytes (short fragments of DNA or xanthan) or spherical micelles of sodium dodecyl sulfate (SDS). Polyanionic cosolutes were then removed by a combination of diffusion and electrophoresis. These processes are expected to yield gels with 'templated' channels having dimensions near those of the double helical polymers (diameters approximately 2-3 nm, lengths of 50-200 nm) or pores near the size of the spherical SDS micelles (approximately 4-5 nm). This hypothesis was tested by comparing the relative electrophoretic mobilities of proteins (3400 to 43,000 Da) complexed with SDS on templated and conventional gels. Differences in electrophoretic mobilities were observed between all templated gels and control normal gels, demonstrating that the templating process altered the polyacrylamide network. No evidence was found for phase separation of cosolutes from the polyacrylamide network during polymerization. Templated pores are expected to enhance the mobilities of molecules in a particular size range relative to smaller and larger molecules. Gels templated with DNA or xanthan (8-10% final concentration) exhibited little size selectivity, but selectivity was observed for gels templated with SDS varied with polyacrylamide concentration in a manner consistent with the creation of templated pores approximately the size of SDS micelles and larger than the average pore size in a surrounding polyacrylamide network.

Comparison of behavior of N-substituted acrylamides and celluloses on double-stranded DNA separations by capillary electrophoresis at 25 degrees and 60 degrees C

The behavior of N-substituted poly(acrylamides) and of cellulose in the separation of double-stranded DNA by capillary zone electrophoresis (CZE) is evaluated. Contrary to previously held belief, which attributed best separations in poly(acrylamides) to small DNA fragments (typically in the 50-1000 bp size range) and in celluloses to large DNA fragments, we show that also celluloses can achieve fine sieving of short DNA sizes provided they are used at much higher concentrations than previously reported. For example, in the case of hydroxyethylcellulose (HEC), typically used at 0.2-0.8% concentrations, levels of 3% produce excellent patterns, at 25 degrees C, in the 50-600 bp size range. If separations are conducted at 60 degrees C, sieving is lost in most liquid polymers. However, if the concentration of HEC is raised to 6% and that of hydroxypropylmethylcellulose (HPMC) above 1%, sieving is fully restored. Also, N-substituted acrylamido derivatives, notably N-acryloylaminoethoxyethanol (AAEE) and N-acryloylaminopropanol (AAP) offer excellent performance at both 25 degrees and 60 degrees C, whereas plain poly(acrylamide) irreversibly collapses at high temperatures, possibly due to intrinsic instability of the amido bond under such harsh conditions. Among all the polymers investigated, an 8% solution of poly(AAP) offers the best performance and highest theoretical plates in the 25 degree-60 degree C interval. Separations at high temperatures are necessary when dealing with detection of point mutations in temperature-programmed CZE and are preferred in DNA sequencing. Two additional advantages are evident when running DNA separations at 60 degrees C: a marked reduction of analysis times and a linearization of the transit times of the larger (434-587 bp) DNA fragments, in all polymers tested.

Use of fluorescence decay times of 8-ANS-protein complexes to study the conformational transitions in proteins which unfold through the molten globule state

The conformational transitions starting with the native protein, passing the molten globule state and finally approaching the unfolded state of proteins was investigated for bovine carbonic anhydrase B (BCAB) and human alpha-lactalbumin (alpha-HLA) by means of fluorescence decay time measurements of the dye 8-anilinonaphthalene-1-sulphonic acid (8-ANS). Stepwise denaturation was realized by using the denaturant guanidinium chloride (GdmCl). It was shown that 8-ANS bound with protein yields a double-exponential fluorescence decay, where both decay times considerably exceed the decay time of free 8-ANS in water. This finding reflects the hydrophobic environment of the dye molecules attached to the proteins. The fluorescence lifetime of the short-time component is affected by protein association and can be effectively quenched by acrylamide, indicating that 8-ANS molecules preferentially bind at the protein surface. The fluorescence lifetime of the long-time component is independent of the protein and acrylamide concentration and may be related to protein-embedded dye molecules. Changes of the long lifetime component upon GdmCl-induced denaturation and unfolding of BCAB and alpha-HLA correlate well with overall changes of the protein conformation. The transition from native protein to the molten globule state is accompanied by an increase of the number of protein-embedded 8-ANS molecules, while the number of dye molecules located at the protein surface decreases. For the transition from the molten globule to the unfolded state was the opposite behaviour observed.

5-Fluorouracil release from copolymeric hydrogels of itaconic acid monoester. I. Acrylamide-co-monomethyl itaconate

The aim of this work was to test the application of new copolymeric poly (acrylamide-co-monomethyl itaconate) (A/MMI) hydrogels to 5-fluorouracil (5-FU) release. Three different compositions of copolymers have been studied, 90A:10MMI 75A:25MMI and 60A:40MMI. The equilibrium swelling degree in saline solution was between 76 and 80% depending on the copolymer composition. 5-FU, as the sodium salt, was trapped in the gels by including it in the feed mixture of polymerization. The swelling kinetics of the hydrogels in saline solution were studied at four temperatures, and the diffusion coefficient and the activation energy of the process were obtained. The 5-FU release as a function of temperature and disc load was studied; the diffusion coefficient and the activation energy of the release process were also obtained. The diffusion studies follow Fick's second law.

Release of 5-fluorouracil from poly(acrylamide-co-monopropyl itaconate) hydrogels

The aim of this work was to test the application of copolymeric poly(acrylamide-co-monopropyl itaconate) (A-MPI) hydrogels on the release of 5-fluorouracil (5-FU). The equilibrium degree of swelling in saline solution was 83 +/- 2%. 5-FU, as the sodium salt, was trapped in gels by placing it in the polymerization feed mixture. The diffusion coefficients for both swelling of the gels and the release of 5-FU were determined, in addition to the activation energies for both processes. To determine the applicability of these copolymers, A-MPI (75:25) gel was subcutaneously implanted in rats and the drug plasma concentration was determined by HPLC.

'Tunable' positive and negative surface charges on a capillary wall: exploiting the Immobiline chemistry

The Immobiline (weak acrylamido acids and bases) chemistry has been applied to the covalent attachment of a positively (or, if needed, negatively) charged layer onto the inner surface of the silica wall. In particular, the following basic Immobilines have been used: pK 6.2, pK 7.0, pK 8.5 and pK 9.3. In order to avoid pK changes, the charged Immobilines are mixed with neutral acrylamido derivatives (in particular the highly resistant and hydrophilic N-acryloyl aminoethoxyethanol) so as to form a co-polymer having a 1:5 molar ratio (charged to neutral). The mu(eo) vs. pH curves have a slope opposite to that of a naked capillary and fan out on the pH scale following the titration curves of the different weak bases. Such chemistry allows the covalent attachment of charged species having known pK values and offering controlled charged densities on the wall. However, with the atomic force microscope, it is found that such soft coatings (whether charged or neutral) do not seem to provide complete coverage of the surface: naked patches of fused silica are found interdispersed among the polymer-coated ones. A good solution is a hybrid bonded and dynamic coating, obtained by adding short chain linear polyacrylamides to the background electrolyte. Good separations of polycations [poly(L-histidine)] and of histones are reported up to pH 5.7.

Complexes of myosin subfragment-1 with adenosine diphosphate and phosphate analogs: probes of active site and protein conformation

Previous work has revealed phosphate-dependent differences in the complexes formed from myosin subfragment-1 with adenosine diphosphate (S1.ADP) and aluminum fluoride (AlF4-) or beryllium fluoride (BeFx) [Phan and Reisler, Biophys. J., 66 (1994) A78], with the former resembling more the S1**.ADP.Pi state while the latter resembles more the S1.ATP state. In this work, the conformations of the S1.epsilon ADP.AlF4- and S1.epsilon ADP.BeFx, complexes were examined by nucleotide chase and collisional quenching experiments. epsilon ADP release from S1.epsilon ADP.AlF4- was slower than that from S1.epsilon ADP.BeFx. However, acrylamide titrations of S1.epsilon ADP.AlF4- and S1.epsilon ADP.BeFx showed little difference in nucleotide protection from quenching between the two complexes. This contrasts with the earlier observation on phosphate analog-dependent changes in the reactivity of the SH1 group on S1. To confirm phosphate-related perturbation of the SH1-SH2 sequence, emission spectra of fluorescein (IAF)-labeled SH1 and IANBD-labeled SH2 were recorded for S1 complexes with nucleotides and phosphate analogs. Considerable differences were found between the BeFx and AlF4- complexes with S1.MgADP for both SH1- and SH2-labeled proteins. These results are consistent with a recent crystallographic study of S1 complexes with ADP and phosphate analogs [Fisher et al., Biophys. J., 68 (1995) 19S] and the idea that the opening of the nucleotide cleft on S1 does not change much during ATP hydrolysis [Franks-Skiba et al., Biochemistry, 33 (1994) 12720], while significant changes in the SH1-SH2 region accompany phosphate cleavage.

Novel acrylamido monomers with higher hydrophilicity and improved hydrolytic stability: II. Properties of N-acryloylaminopropanol

The physico-chemical properties and the electrophoretic behavior of the novel set of monomers reported by (Simò-Alfonso et al., Electrophoresis 1996, 17, 723-731) have been evaluated. Of utmost importance was the combination of high hydrophilicity and extreme hydrolytic stability, most desired properties for, any electrophoretic matrix, especially for protein fractionation. One of these monomers (N-acryloylaminopropanol, AAP) was found indeed to be extremely hydrophilic (with a partition coefficient P of only 0.10, vs. P = 0.13 for N-acryloylaminoethoxyethanol and P = 0.20 for acrylamide) and to possess excellent stability to alkaline hydrolysis. Its hydrolysis constant (0.008 L mol-1 min-1), as a free monomer, in an alkaline milieu, was found to be about one order of magnitude lower than conventional acrylamide (0.05 L mol-1 min-1). In the polymer state, the resistance to hydrolysis of poly(AAP) was assessed as 500 times greater than a conventional poly(acrylamide) matrix.

Quantification and in vitro toxicity studies of extractable chemicals from synthetic ion exchangers

Soluble chemicals extracted from chromatographic media can contaminate pure biological preparations. These contaminants, which may come from the chemical synthesis of the polymers, could have adverse effects as far as their toxicity is concerned. Ion exchangers made using classical acrylic monomers have been investigated for the presence of traces of monomers which are not converted into polymers. In vitro toxicity investigations have also been performed with the same monomers. The obtained data showed that the amount of free residual monomers was below the sensitivity of the analytical methods (HPLC) for both the main monomers (acidic and alkaline) and the acrylic bifunctional monomer. Toxicity trials showed no adverse effects on human cells in culture. Moreover, no polyploidia induction was evidenced in cells cultured in the presence of monomers.

Time-resolved fluorescence study of a calcium-induced conformational change in prothrombin fragment 1

The wavelength dependent fluorescence decay properties of bovine prothrombin fragment 1 have been investigated employing a picosecond time-correlated single photon counting technique. All observations are discussed with using the crystal structure (Soriano-Garcia et al., Biochemistry 31:2554-2566, 1992). Fluorescence lifetimes distribution and conventional multiexponential analysis, as well as acrylamide quenching studies lead to the identification of six distinguishable tryptophan excited-states. Accessibility to the quencher and the known structure are used to associate a fluorescence decay of the tryptophan present in the Gla domain (Trp42) with two red shifted components (2.3 and 4.9 ns). The two kringle domain tryptophans (Trp90 and Trp126) exhibit four decay times (0.06, 0.24, 0.68, and 2.3 ns), which are blue shifted. The calcium-induced fluorescence quenching is a result of static quenching: the five decay times remain unchanged, whereas the fluorescence intensity of Trp42 is decreased. The static quenching process is a consequence of a ground state interaction between the Cys18-Cys23 disulfide bridge and Trp42. The monomolecular equilibrium constant for this disulfide-pi-electron interaction is found as 4.8.

Estimation of average depth of penetration of melanotropins in dimyristoylphosphatidylglycerol vesicles

The interaction of alpha-melanocyte stimulating hormone (alpha-MSH) and its analogs [Nle4,D-Phe7]-alpha-MSH (MSH-I) and [Nle4,Asp5,D-Phe7,Lys10]-alpha-MSH(4-10) (MSH-II) with vesicles of dimyristoylphosphatidylglycerol (DMPG) was studied by steady-state fluorescence spectroscopy. The association constants for the interaction were obtained from binding isotherms. Electrostatic effects on the interaction were taken into account through calculation of Gouy-Chapman potentials. The quenching of fluorescence of the peptides by acrylamide and nitroxide labeled lipids demonstrated that insertion of the peptides into the lipid phase of the vesicles causes the changes in the hormone's fluorescence in the presence of DMPG. The parallax method was employed for the estimation of an average depth of penetration of the peptides in the DMPG vesicles. It was found that the Trp residue in alpha-MSH and in MSH-II is positioned around the carbons 6 and 8 of the aliphatic chain. The analog MSH-I goes deeper into the bilayer compared to the others peptides, and the Trp residue locates between carbons 10 and 11 of the acyl chain. The average depth of penetration shows correlation with the number of lipid molecules that interact with one molecule of peptide. There is no direct correlation between the association constants for the lipid-peptide interactions and the depth of penetration of the hormone.

Partially-hydrophobized polymer particles derived from N,N-dimethylaminopropylacrylamide for endotoxin removal from acidic protein solution

Novel copolymeric adsorbents for the selective removal of endotoxin from an acidic protein solution were prepared. The adsorbents comprise spherical copolymers derived from N,N-dimethylaminopropylacrylamide (DMAPAA) and divinylbenzene (DVB). When the molar ratio of DMAPAA to DVB was 80/20 (amino-group content: 5.1 meq/g) and the pore size (molecular mass exclusion of polysaccharide, Mlim) was 4000 to 10000, DMAPAA/DVB showed high endotoxin-adsorbing activity at pH 5.0 to 9.0 and ionic strengths of mu = 0.05 to 0.4. The capacity of the adsorbent (Mlim: 4000) was 390 micrograms of endotoxin (lipopolysaccharide purified from E. coli O111:B4) per ml of the adsorbent using the batchwise method. The apparent dissociation constant between endotoxin and the adsorbent was 2.2 x 10(-12) M. On the other hand, the adsorption of bovine serum albumin, an acidic protein, by the adsorbent increased with an increase in Mlim from 4000 to 10000, but decreased with an increase in ionic strength (mu) from 0.05 to 0.2. As a result, DMAPAA/DVB (80/20) (Mlim: 4000) selectively removed endotoxin from various acidic protein solutions at pH 7.0 and mu = 0.05. The residual concentration of endotoxin in the protein solution always decreased to a concentration lower than 0.1 ng/ml, and recovery of the protein was more than 97%.

Temperature and pH-sensitive polymers for human calcitonin delivery

PURPOSE

Stimuli-sensitive polymers are suitable candidates for oral peptide drug delivery vehicles since they will prevent gastric degradation in the stomach while providing a controlled release of a peptide drug such as calcitonin later. The purpose of this study was to fabricate polymeric beads from pH/temperature sensitive linear terpolymers (poly(N-isopropylacrylamide-co-butylmethacrylate-co-acrylic acid) and load them with a peptide drug, human calcitonin, which was dissolved in aqueous phase.

METHODS

The polymeric beads were formed by solubilizing a cold, aqueous solution of temperature sensitive polymer with human calcitonin. This solution was added dropwise into an oil bath kept at a temperature above the LCST of a polymer, precipitating polymer and entrapping the peptide. The quantity and the physical state of the peptide were analyzed by reverse-phase HPLC, CD and FTIR and its biological activity after loading was determined in vivo.

RESULTS

The loading efficiency and stability of human calcitonin into the polymeric beads was studied as a function of pH and ionic strength of the loading buffer and temperature of the oil bath. Final optimal loading conditions were 20 mM glycine/HCl buffer, pH 3.0 containing 0.15 M NaCl as a dissolution medium and 23 degrees C as the oil bath temperature. Loading and release of human calcitonin were also studied as a function of acrylic acid content in the terpolymers. As the acrylic acid content increased from 0 to 10 mol %, the loading efficiency and stability of calcitonin improved significantly. The same trend was observed for the quantity of released calcitonin. In vivo biological activity of the released hormone was preserved.

CONCLUSIONS

The results showed that the beads made of the polymers with high content of acrylic acid (most hydrophilic) provided better loading, stability and release of human calcitonin. The designed beads represent a new potential system for oral delivery of calcitonin and other peptides.

A possible tertiary structure change induced by acrylamide in the DNA-binding domain of the Tn10-encoded Tet repressor. A fluorescence study

A thorough investigation of the acrylamide fluorescence quenching of F75TetR, a mutant of the Tn10-encoded TetR repressor containing a single Trp residue at position 43, was carried out. The Trp-43 residue is located in a helix alpha-turn-helix alpha (H-t-H) motif involved in the specific binding of F75TetR to the operator site in specific DNA. Distinct Ranges of acrylamide concentration have been assumed. At acrylamide concentrations below 0.15-0.2 M (a usual range of values in fluorescence quenching studies) the observed limited tertiary structure change induced by acrylamide is consistent with a noncooperative local unfolding of the DNA-binding domain. It is suggested that penetration of the neutral quencher could cause the deletion of a hydrophobic tertiary structure contact, partly involving TrP-43, responsible for the anchoring of the H-t-H motif inside the three-helix protein bundle, characterizing the N-terminal part. Correspondingly, the affinity of the mutant repressor for the operator was shown to decrease substantially (about five orders of magnitude), seemingly losing its specificity. A subsequent phase, up to 0.8 M acrylamide, was observed in which the involved intermediate protein structure is not further perturbed, nor is DNA binding.

In vitro swelling studies and preliminary biocompatibility evaluation of acrylamide-based hydrogels

In this in vitro study, the biocompatibility of acrylamide-based hydrogels such as acrylamide/crotonic and acrylamide/itaconic acid, prepared by using gamma-rays, has been investigated against some biochemical parameters of human serum. The swelling kinetics of acrylamide/crotonic and acrylamide/itaconic acid hydrogels are investigated in distilled water and physiological saline solution and some swelling and diffusion parameters have been calculated. For the analysis of biocompatibility, acrylamide/crotonic and acrylamide/itaconic acid hydrogels are incubated in 10 different human sera for 24 h and their biocompatibilities with some biochemical parameters have been investigated. No significant difference in values before and after the test procedures have been found. It is therefore concluded that acrylamide/crotonic and acrylamide/itaconic acid hydrogels are biocompatible.

Hemocompatible properties of polymeric derivative of paracetamol

Copolymerization of N,N-dimethylacrylamide (DMAA) and p-acryloyloxiacetanilide (AOA) was carried out at different mole ratios of the monomers to obtain copolymers of varying compositions. DMAA contents were very near to the corresponding monomer feed and varied between 0.20 and 0.80. Investigation of the protein adsorption of these polymer surfaces showed that copolymers with higher DMAA content adsorbed more albumin than fibrinogen. The scanning electron micrographs of the polymer-coated coverslips after contact with blood showed an antithrombogenic behaviour of these surfaces.

Intercomparison of DNA sizing ladders in electrophoretic separation matrices and their potential for accurate typing of the D1S8O locus

The 100-1,000 basepair size typical of PCR-amplified DNA fragments demands high resolution electrophoretic gels for the adequate characterization of small differences among samples. We have studied the behavior of a number of commercial sizing ladders in three classes of separation systems: polyacrylamides with discontinuous buffer, proprietary acrylamides with continuous buffer, and agarose-like materials with continuous buffer. None of the ladders examined perform adequately in any of these systems using vendor-supplied nominal ladder component basepair sizes. All ladders successfully typed D1S8O alleles after calibration with the allelic ladder (replacing the nominal size values with the least squares estimate of allele/matrix-specific apparent sizes). Some ladders and matrices are qualitatively better than others. No one ladder proved consistently better than others; a polyacrylamide gel with ribose modifier provided the most precise results in this study. Appropriately calibrated electrophoretic apparent sizes must be used for results to be validly exchanged among laboratories. Appropriate allelic ladders or a well defined subset of known alleles can serve as the calibration system.

Endothelial cell differentiation into capillary structures by copolymer surfaces with phenylboronic acid groups

A ternary copolymer composed of m-acrylamidophenylboronic acid, N,N-dimethylaminopropylmethacrylamide and N-isopropylacrylamide was synthesized. Long-term culture of bovine aortic endothelial cells on this copolymer substrate demonstrated adhesion and proliferation of the cells. After 26 days in culture, endothelial cells spontaneously developed into capillary networks. The interactions between phenylboronic acid groups in copolymer and glycoconjugates on endothelial cell plasma membranes are proposed to regulate the induction of tissue formation, since phenylboronic acid groups are known to specifically form reversible complexes with cis-diol compounds such as glucose. This copolymer is a novel material capable of mediating specific signals analogous to extracellular matrix to promote proliferation of endothelial cells, inducing capillary structures and prompt angiogenesis.

Lophozozymus pictor toxin: a fluorescent structural isomer of palytoxin

Purified Lophozozymus pictor toxin (LPTX) shares many properties similar to palytoxin (PTX). LPTX and palytoxin isolated from Palythoa caribaeorum (C-PTX) have similar mol. wts of approx. 2680 on ionspray mass spectrometry (MS). In addition, antibodies against PTX could recognize and bind LPTX. Mixed mode high-performance liquid chromatography (HPLC) of LPTX, C-PTX and H-PTX (isolated from Palythoa tuberculosa) showed a major PTX component common to all three with the characteristic PTX-like UV spectrum at a retention time (Rt) of 17 min. However, LPTX exhibits fluorescence but PTX of equivalent toxicity does not. LPTX showed a unique peak at Rt of approx. 22 min on mixed mode HPLC. In addition, LPTX and C-PTX showed different ion fragmentation patterns on MS/MS. These results suggest that LPTX and the palytoxins are structural isomers, containing at least one difference which gives rise to fluorescence in LPTX.

Cholesterol interaction with recombinant human sterol carrier protein-2

The interaction of human recombinant sterol carrier protein-2 (SCP-2) with sterols was examined. Two independent ligand binding methods, Lipidex 1000 binding of [3H]cholesterol and a fluorescent dehydroergosterol binding assay, were used to determine the affinity of SCP-2 for sterols. Binding analysis indicated SCP-2 bound [3H]cholesterol and dehydroergosterol with a Kd of 0.3 and 1.7 microM, respectively, and suggested the presence of a single binding site. Phase fluorometry and circular dichroism were used to characterize the SCP-2 sterol binding site. Alterations in dehydroergosterol lifetime, SCP-2 tryptophan lifetime, and SCP-2 tryptophan quenching by acrylamide upon cholesterol binding demonstrated a shielding of the SCP-2 tryptophan from the aqueous solvent by bound sterol. Differential polarized phase fluorometry revealed decreased SCP-2 tryptophan rotational correlation time upon cholesterol binding. Circular dichroism of SCP-2 indicated that cholesterol elicited a small decrease in SCP-2 alpha helical content. The data suggest that SCP-2 binds sterols with affinity consistent with a lipid transfer protein that may act either as an aqueous carrier or at a membrane surface to enhance sterol desorption.

A lifetime oncogenicity study in rats with acrylamide

A lifetime oncogenicity study in Fischer 344 rats was conducted to accurately characterize the carcinogenic potency of acrylamide. Acrylamide was administered in drinking water throughout the 106-week study at concentrations required to provide a dose of 0, 0.1, 0.5, or 2.0 mg/kg/day to males or 0, 1.0, or 3.0 mg/kg/day to females. Complete necropsy and gross pathology examinations were performed on all study animals. Histopathology examinations were conducted on selected tissues of all high-dose and control animals. Selected tissues from intermediate and low-dose groups were subjected to histopathological examinations as required to clarify high- and control-dose group observations. There was no visual observation of neurotoxicity in any study animal but sciatic nerve degeneration was observed in the male and female high-dose groups. Increased mortality related to acrylamide was observed in the high-dose male group from Month 17 to the end of the study and in the high-dose females during Month 24. Mesotheliomas of the testicular tunic were significantly increased in the high-dose male group. The combined incidence of mammary gland adenocarcinomas and fibroadenomas was significantly increased in both acrylamide-dosed female groups. Males and females in the high-dose groups as well as females of the low-dose group had significantly (p < 0.001) increased thyroid follicular cell adenomas and adenocarcinomas. A variety of other tumor types observed with increased incidence in a previous acrylamide oncogenicity study (i.e., combined CNS glial neoplasms, papillomas of the oral cavity, adenomas of the clitoral gland, and uterine adenocarcinomas) were not observed to be present at increased incidence in this study. This study confirms previously described acrylamide induction of benign tumors of the thyroid and mammary glands as well as mesotheliomas of the testis. By using a larger number of animals with an unbalanced study design, this study showed that acrylamide did not induce glial tumors and demonstrated that the no-observable-effect level for scrotal mesotheliomas is 0.5 mg/kg. It also demonstrated that the increased incidence of mammary tumors was again within historical control ranges.

Antibody-targeted polymer-bound drugs

Drug targeting is an attractive new approach to killing cancer cells while leaving normal tissue unharmed. Recently we have developed a new generation of antibody-targeted immunosuppressive (cyclosporin A) and cytostatic (daunomycin, doxorubicin) drugs and photosensitizers (chlorin e6) effective in vitro and in vivo. The drugs and the targeting antibody (polyclonal and monoclonal) are conjugated to the oligopeptidic side chains of a water-soluble synthetic carrier, copolymer of N-(2-hydroxypropyl)methacrylamide. The composition of the side chains ensures the stability of the linkage between the drug and the polymeric carrier in the bloodstream and its intralysosomal degradability which is a prerequisite for the pharmacological activity of the preparation. Antibody-targeted polymer bound drugs show considerably decreased hepatotoxicity, cardiotoxicity, myelotoxicity and nephrotoxicity. Two adriamycin-HPMA copolymers are in Phase I/II clinical trials in United Kingdom.

Effect of temperature and duration of post-cure on in vitro wear and quantity of remaining double bonds of resins containing carboxylic anhydride

The present study determined the effect of post-cure temperature and duration on in vitro wear resistance and quantity of remaining double bonds of anhydride-containing resins. Temperatures were varied between 37 degrees C and 225 degrees C, and durations were varied between 0 and 24 h. The quantity of remaining double bonds could not be established for post-cure temperatures of 200 degrees C or more due to melting of the polymer. A temperature of approximately 120 degrees C had optimal effect on wear resistance. Quantity of remaining double bonds and wear were found to decrease with increasing duration of post-cure. Low quantities of remaining double bonds were generally associated with low in vitro wear.

[Biological monitoring of exposure to alkylating xenobiotics by determining them using a new analytical approach in complexes with hemoglobin, plasma proteins and mercapturic acids in urine. II. Acrylamide]

A new simple and prompt procedure for measuring acrylamide (propenamide, PA) in PA-derived mercapturic acid, such as N-acetyl-S-(2-propenamide)-L-cysteine (N-Ac-PAC), and in hemoglobin (Hb) and plasma protein adducts in the rats expose to PA was developed, by employing gas chromatography (GC). PA in mercapturic acids or proteins was liberated on high-temperature heating in an injector port during the working procedure of a GC capillary after preoxidation of sulfur atoms in PA-bound cysteine to a sulfoxide form with hydrogen peroxide and analyzed. This method resulted in 87% of PA in authentic N-Ac-PAC. The number of PA released from the protein adducts was proportional to the cumulative dose of PA given at a concentration of 1-75 mg/kg during 1-3 weeks. The alkylating level of Hb was approximately 65 times higher than that of plasma proteins and it was nearly 6.5% of its cumulative dose. The index of binding to Hb and the rate of its alkylation were 163 and 0.75.10(-3) liter/g-1/hour-1, respectively.

Interaction of palytoxin with red cells: structure-function studies

Palytoxin (PTX), a potent toxin isolated from the marine soft coral Palythoa tuberculosa increases the cationic permeability of red cell membranes and inhibits the (Na+,K+)-activated ATPase, effects that are completely reversed by ouabain. It has also been shown to compete with ouabain for a binding site and it has been suggested that it binds to the Na+,K(+)-pump molecule in cells. In a search for analogues of PTX that would bind covalently and could thus be used to identify and characterize the binding site, we have used compounds which differed from PTX at one end or at both ends simultaneously. In order to determine whether these derivatives could be used to replace palytoxin, we tested their potency to induce an increased cation flux, complete with ouabain for its binding site, and inhibit the isolated, purified (Na+,K(+)-ATPase). The results obtained indicate that departures from the PTX structure at one end or at both ends simultaneously substantially decrease the ability of the compounds to increase the cationic permeability of red blood cells and to inhibit the (Na+,K(+)-ATPase). These actions were found to be completely reversed by ouabain, but the analogues are two to three orders of magnitude less potent than PTX in competing with ouabain for its binding site. These results suggest that both ends of the palytoxin molecule participate in the interactions of the toxin with its receptor and that modifications in these regions of the molecule produce significant alterations in its binding and subsequent action on red cell membranes.

Cell attachment to laser-induced AAm- and HEMA-grafted ethylene-propylene rubber as biomaterial: in vivo study

With the purpose of improved tissue compatibility, ethylene-propylene rubber (EPR)-based vulcanizates have been surface grafted with acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA) using CO2-pulsed laser as excitation source. Grafted surfaces were characterized by performing scanning electron microscopy combined with energy dispersive X-ray analysis and attenuated total reflectance infrared spectroscopy to study the surface morphology and grafting. Surface hydrophilicity (measured by water drop contact angle) increased for the grafted samples. Fractal type of morphology is formed by the grafted poly(AAm) and poly(HEMA) chains on the surface of EPR, which provides both hydrophilic and hydrophobic sites. In vivo tissue compatibility was assessed by implanting test samples in the deep intramuscular and peritoneal layers of rabbits. After 8 weeks of implantation, comparative results indicate that the adhesion of macrophages to EPR samples modified with AAm and HEMA, with no respiratory burst and cellular damage, is significantly lower than their adhesion on unmodified surfaces which show an activated state of the attached macrophages. Also, no acute or chronic inflammatory reaction was observed at the site of implantation and a thinner fibrous tissue capsule formed around the modified samples, whereas foreign body giant cells adhered to unmodified EPR.

Role of the C-terminal tail region in the self-assembly of lambda-repressor

Acrylamide quenching of the tryptophan fluorescence of the lambda-repressor at different protein concentrations indicates that one of the three tryptophan residues, W129, W142, and W230, undergoes a change in environment upon self-assembly, from dimer to associated species. Quenching data suggest that this tryptophan residue is inaccessible to low concentrations of acrylamide and is blue-shifted in the associated form. In the dimer, this tryptophan residue is highly accessible to acrylamide and is red-shifted. NBS oxidation, at protein concentrations which favor the associated form, showed that this tryptophan is also significantly protected from NBS oxidation. HPLC peptide mapping of NBS-oxidized lambda-repressor, amino acid analysis, and sequencing indicate that the protected, blue-shifted tryptophan is tryptophan 230. A mutant repressor (F235C) was specifically labeled at Cys 235 with an environment-sensitive probe, acrylodan. The acrylodan fluorescence of the labeled F235C lambda-repressor undergoes a significant blue-shift, accompanied by fluorescence enhancement, upon protein association. Along with other genetic evidence, these results suggest involvement of the C-terminal tail region in the self-assembly of the lambda-repressor.

[Effect of radiation on erythrocyte membrane protein structure]

Influence of the 5 MeV electron beam on the structural dynamic organization of the protein phase of erythrocyte shadows has been studied by suppression of the tryptophane fluorescence of proteins by acrylamide. It has been observed that the irradiation leads to conformation changes and increase of the structural rigidity of the protein molecules.

Analysis of glycosaminoglycan-degrading enzymes by substrate gel electrophoresis (zymography)

Substrate gel electrophoresis is of use for detecting minute amounts of hyaluronidase (HAase). In substrate gel electrophoresis, hyaluronan (HA) is impregnated in a gel. To determine the presence of degradation enzymes for other glycosaminoglycans (GAGs), the sizes of whose molecules are much smaller than that of HA, we have developed a technique by which chondroitin sulfate (CS) is chemically modified by introducing an allyl group at the reducing end for its immobilization in the gel. Enzymes with CS-degrading activity were detected on a CS-copolymerized gel in the presence or absence of sodium dodecyl sulfate. The smallest amount of chondroitinase ABC and HAase was found to be 8 microU and 0.35 mU, respectively. By zymography using HA-impregnated and modified CS-copolymerized gels human serum HAase has been shown to consist of at least two isoforms each with its own substrate specificity. Using this method, uterine tumor tissue has been shown to secrete a novel HAase which degrades HA at neutral pH, but not CS at any pH. This method was also confirmed applicable to other GAGs for determining individual GAG-degrading enzymes. In future research, it will be used to examine the regulation of each GAG species in tissue.

Fluorescence analysis of the interaction between ganglioside GM1-containing phospholipid vesicles and the B subunit of cholera toxin

Binding of cholera toxin B protomer (CT-B) to a pyrene-labeled analogue of its ganglioside GM1 receptor (pyrene-GM1) in the absence and presence of phosphatidylcholine vesicles was monitored using steady-state fluorescence spectroscopy. CT-B association with pyrene-GM1 micelles induces changes in the fluorescence properties of this ganglioside analogue that are consistent with its conversion from an excimer to a monomer form. Incubation of pyrene-GM1 with preformed vesicles of phosphatidylcholine (PC) results in complete conversion of pyrene-GM1 to its monomer form, however, unlike with CT-B binding, incorporation of pyrene-GM1 into PC vesicles occurs with a concomitant loss of fluorescence quenching by the small polar quenching agent acrylamide. Subsequent binding of CT-B to the PC-GM1 composite vesicles causes no further change in the pyrene fluorescence emission spectrum but does appear to increase acrylamide accessibility. These data lead to the conclusion that cholera toxin binding to a cell membrane alters membrane packing at the site of attachment. Furthermore, this phenomenon appears to be influenced by environmental conditions such as pH. A pH of about 4.0 or less causes acrylamide quenching to decrease to approximately the levels observed in the absence of CT-B. These results may be useful in describing the dynamics of the interaction between cholera toxin and target cell membranes. Moreover, these data could provide clues to the mechanism by which the toxic portion of CT is able to enter the cytoplasm of target cells.

Use of sialylated or sulfated derivatives and acrylamide copolymers of Gal beta 1,3GalNAc alpha- and GalNAc alpha- to determine the specificities of blood group T- and Tn-specific lectins and the copolymers to measure anti-T and anti-Tn antibody levels in cancer patients

Sialylated or sulfated derivatives and acrylamide copolymers of blood group T-(Gal beta 1,3GalNAc alpha-) and Tn-(GalNAc alpha) haptens were studied for their interaction with the lectins of peanut (PNA), Agaricus bisporus-(ABA), Helix pomatia-(HPA) and Vicia villosa B4-(VVA), using asialo Cowper's gland mucin (ACGM), which contains both T and Tn epitopes, as the coating substrate in enzyme linked lectin assay. Both T and Tn copolymers (-40 haptens) showed high affinity and strict specificity; although the T-copolymer at 0.05-0.07 microM concentration caused 50% inhibition of interaction of either PNA or ABA with ACGM, there was little inhibition of the HPA and VVA interactions even at over 100 times that concentration. The Tn-copolymer at 0.02-0.05 microM inhibited HPA or VVA interaction with ACGM by 50% but gave virtually no inhibition of PNA and ABA binding. Sialyl, sulfate or methyl group substitution on C-6 of GalNAc of the T-haptene did not prevent interaction with PNA but almost abolished interaction with ABA. In contrast, sialyl or sulfate group on C-6 and sulfate on C-3 of Gal in Gal beta 1,3GalNAc alpha- inhibited almost completely the interaction of PNA with ACGM but had only a slight effect on the interaction of ABA; C-6 substitution with either sialic acid or sulfate on GalNAc alpha- almost abolished the interaction of both HPA and VVA with ACGM.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the adherence energy of experimental resin cements bonded to a nickel-chromium alloy

Reliable adherence of resin-based cements is of prime importance for the longevity of cemented restorations. The present study investigated whether a relationship exists between adherence energy to a metal substrate and the degree of cross-linking and wetting characteristics of resin-based luting agents. The adherence energies between a sand-blasted metal surface and a series of experimental resin cements were measured by means of the wedge test. The degree of cross-linking was calculated from the monomer composition of the resin cements. The measured wetting characteristics were work of adhesion and surface tension, and their dispersive and polar components. Adherence energy varied between 22 and 81 J/m2 and was influenced by the nature of the resin cements: Those with a low degree of cross-linking resulted in high adherence values. Furthermore, resin cements whose monomers were relatively polar gave rise to high adherence values. Although other metals may not behave in exactly the same way, these results may help in the formulation of new, more retentive resin cements.

Biochemo-mechanical function of urease-loaded gels

A gel system is developed that undergoes a reversible volume phase transition in response to a small amount of urea. An N-isopropylacrylamide gel in which urease is immobilized by entrapping changes its equilibrium volume discontinuously when urea molecules are hydrolyzed by urease causing a change in pH that alters the osmotic balance of the gel triggering the phase transition. The system demonstrates a method of mechano-biochemical transformation where molecular recognition and biochemical reaction are achieved by an enzyme and the macroscopic amplification of the reaction is carried out by a gel capable of a volume phase transition. The work presented here is dedicated to Professor Allan S. Hoffman to honor his 60th birthday and his pioneering contribution to the science and technology of polymer gels, both as a scientist and as an educator.

A new method for in vitro calcification using acrylamide gel and bovine serum

To investigate the mechanism of biological calcification in vitro, a model system consisting of an acrylamide gel block (1 x 3 x 3 mm) and fetal bovine serum was developed. Mineral deposition was induced in gel blocks which were immersed in 300 microliters of fetal bovine serum at 37 degrees C for 7 days in a CO2 incubator. X-ray diffraction indicated that the mineral was hydroxyapatite with low crystallinity. Effects of the concentration of acrylamide gel, the partial pressure of CO2 and matrix proteins within the gel on the mineral formation were investigated. In the gel concentration range of 10-60%, the largest amount of crystal grew in 40% acrylamide gel, where the serum protein did not penetrate. With an increase in the partial pressure of CO2 the Ca content in the gel block increased, reached the highest level at about 3.5% CO2 and then began to decrease. In 40% gel and at 5% CO2, the mineral formation was enhanced by phosvitin, phosphophoryn, demineralized dentin powder and alkaline phosphatase. Mineral deposition occurred around the collagen fibers immobilized in 40% acrylamide gel. These results indicate that 1) a putatively serum-derived inhibitor of calcification with high-molecular weight was prevented from penetrating into the 40% acrylamide gels, 2) immobilized polyanionic proteins and alkaline phosphatase were able to increase mineral deposition and 3) the partial pressure of CO2 greatly influenced the mineral deposition. It was concluded that this gel system is useful to investigate the mechanism of biological calcification in vitro.

Modulating the phase transition temperature and thermosensitivity in N-isopropylacrylamide copolymer gels

Temperature-responsive copolymer (or ternary copolymer) gels of N-isopropylacrylamide (IPAAm) were synthesized with hydrophobic alkyl methacrylate (RMA), hydrophilic acrylamide (AAm), N,N'-dimethylacrylamide (DMAAm), and N-acryloylpyrrolidine (APy) as comonomers. The effects of these comonomers on the phase transition temperature (LCST) and the thermosensitivity have been discussed. The LCST of poly(IPAAm) gel in phosphate buffered saline (PBS) was lowered by the introduction of hydrophobic RMA, and the change in equilibrium swelling ratio with temperature change became smaller with an increase in RMA content. However, a stable skin layer to achieve complete 'on-off' regulation of drug release was formed at a higher temperature by RMA due to hydrophobic interaction of alkyl chains. The LCST of poly(IPAAm-co-AAm) gel increased with an increase in AAm content. However, the thermosensitivity of the gel became smaller. It was suggested that hydrophilic AAm prevented the formation of a dense skin layer at a higher temperature. It was difficult to obtain a complete 'off' state due to an insufficiently dense skin layer in order to stop the drug release. The LCST was raised and great thermosensitivity was possible by the introduction of DMAAm or APy. Poly(IPAAm-co-DMAAm) enabled 'on-off' drug release in response to smaller temperature changes around the body temperature. The molecular design to control transition temperature and thermosensitivity of gel was established.

Development of nonpolar surfaces in the folding of Escherichia coli dihydrofolate reductase detected by 1-anilinonaphthalene-8-sulfonate binding

The development of nonpolar surfaces during the folding of Escherichia coli dihydrofolate reductase (DHFR) was studied by monitoring the time-dependent fluorescence of 1-anilinonaphthalene-8-sulfonate (ANS) included in the refolding solution. Stopped-flow refolding experiments demonstrated a rapid increase in fluorescence intensity within the dead time of mixing (5 ms), indicating that the earliest detectable folding intermediate contains hydrophobic surfaces which are capable of binding ANS. A further increase in fluorescence intensity over the next 300 ms coincides with the formation of a set of four intermediates which are known to contain a specific tertiary contact [Kuwajima, K., Garvey, E. P., Finn, B. E., Matthews, C. R., & Sugai, S. (1991) Biochemistry 30, 7693-7703]. Experiments performed in the presence of polar fluorescence quenching agents indicate that the binding sites for ANS in the burst phase species are more exposed to solvent than those in the subsequent set of intermediates. When considered along with the above study of the formation of secondary structure by stopped-flow circular dichroism, these results imply that DHFR initially forms a molten globule intermediate. Subdomains containing specific tertiary structure and more solvent-excluded ANS binding sites then form before ultimately being converted to native or native-like conformations during the rate-limiting steps in the folding of DHFR. The occurrence of similar kinetic phases observed by ANS binding during the folding of a number of other proteins suggests that this may be a common scheme for protein folding reactions.

Close proximity of tryptophan residues and ATP-binding site in Escherichia coli primary replicative helicase DnaB protein. Molecular topography of the enzyme

The binding of fluorescent nucleotide analogs to the Escherichia coli primary replicative helicase DnaB protein causes strong quenching of protein tryptophan fluorescence. It results from the efficient fluorescence energy transfer (E) from tryptophans to analogs bound in the nucleotide-binding site, indicating that protein tryptophans are "clustered" in close proximity to the binding site. This is in contrast to the lack of detectable energy transfer to the fluorescent single-stranded DNA (ssDNA) derivative, suggesting a distant separation between two function-linked structural elements of the enzyme, the nucleotide- and ssDNA-binding sites. The dependence of E upon the average number of bound nucleotides/DnaB hexamer is nonlinear, implying a larger separation between tryptophans and the bound nucleotide in the low affinity sites. Spectroscopic studies reveal that tryptophan residues are located on the surface of the DnaB helicase in a hydrophobic cleft, whereas the environment of the tyrosines is heterogeneous, with 6 out of 10 tyrosine residues located on the surface of the helicase. The efficiency of the fluorescence energy transfer from the tyrosines to tryptophans suggests that the "centers of mass" of the residues are separated, possibly reflecting the separation of the nucleotide- and ssDNA-binding sites, with tyrosines constituting part of the ssDNA-binding region.

Interaction of tryptophan residues of cytochrome P450scc with a highly specific fluorescence quencher, a substrate analogue, compared to acrylamide and iodide

The cytochrome P450scc tryptophan fluorescence was studied by the use of the three quenchers acrylamide, 25-doxyl-27-nor-cholesterol (CNO) and potassium iodide (KI). All the nine tryptophan residues were accessible to acrylamide. Whereas a strong interaction (static quenching) between acrylamide and tryptophan in the active site had been found previously for cytochrome P450c21 [Narasimhulu, S. (1988) Biochemistry 27, 1147-1153], in the case of P450scc the temperature dependence of the slope of the linear Stern-Volmer plots indicated a dynamic quenching mechanism. This mechanism was confirmed by fluorescence lifetime measurements. Of the three observed life-times tau 1 = 3.1 +/- 0.5 ns, tau 2 = 0.7 +/- 0.25 ns and tau 3 = 20 +/- 10 ps, tau 1 decreased noticeably as a function of the acrylamide concentration. CNO, a spin-labeled substrate which is known to bind tightly to the substrate-binding site of P450scc, quenched 15.5% of the total fluorescence. The Lehrer plot of this compound indicated a static quenching process with a reciprocal quenching constant of 1/Ks = 4 microM, a value which is in accord with the dissociation constant. Our data indicate that CNO quenches selectively one or two tryptophan residue(s) in the active site. The fluorescence spectrum of the residue(s) accessible to CNO was characterized by a red-shifted emission maximum (from 332 nm to 336 nm). The same residue(s) appeared to be quenched by potassium iodide, although much less effectively (1/Ks = 0.12 M). The most probable candidate for a complex formation with CNO is Trp417, which is rather close to Cys422 (the fifth heme ligand). Four arginine residues (Arg411, Arg420, Arg425 and Arg426) in the heme peptide may constitute the iodide-binding site.

Coupling between external viscosity and the intramolecular dynamics of ribonuclease T1: a two-phase model for the quenching of protein fluorescence

Our recent equilibrium dialysis studies showed that proteins are able to interact preferentially with acrylamide (Punyiczki et al. (1993) Biophys. Chem. 47, 9-19). The presence of considerable amounts of acrylamide--albeit weakly bound--in the protein volume, coupled with the failure of a simple gating model of quenching to rationalise viscosity dependence of the quenching of tryptophan (Trp) fluorescence in Ribonuclease T1 (RNase T1) has prompted us to explore a new model, the two-phase model for quenching. According to this model, the dynamic quenching is accomplished by quencher molecules already in the protein phase at the moment of excitation. Some of the molecules may, at this moment, form an encounter complex with the fluorophore and thus be responsible for the observed static contribution. We use the rate equation derived from our model to study the viscosity dependence of acrylamide quenching of Trp fluorescence in RNase T1. The model allows us to separate co-solvent effects: the chemical effect on the protein and on the distribution of quencher molecules between the bulk and the protein phases and, further, the viscosity effect due to coupling between the bulk viscosity and the local friction affecting intramolecular fluctuations of the protein matrix. We express local friction in terms of bulk viscosity, eta, and a coupling constant kappa (friction = eta kappa). Addition of glycerol up to 65% is characterised by a kappa of 0.50. The viscosity dependence of the apparent bimolecular quenching constant is a combination of two compensating effects: changes in chemical activity and changes in patterns of structural fluctuations.