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PubMed2006

Redox polymer and probe DNA tethered to gold electrodes for enzyme-amplified amperometric detection of DNA hybridization.

The detection of nucleic acids based upon recognition surfaces formed by co-immobilization of a redox polymer mediator and DNA probe sequences on gold electrodes is described. The recognition surface consists of a redox polymer, [Os(2,2'-bipyridine)2(polyvinylimidazole)(10)Cl](+/2+), and a model single DNA strand cross-linked and tethered to a gold electrode via an anchoring self-assembled monolayer (SAM) of cysteamine. Hybridization between the immobilized probe DNA of the recognition surface and a biotin-conjugated target DNA sequence (designed from the ssrA gene of Listeria monocytogenes), followed by addition of an enzyme (glucose oxidase)-avidin conjugate, results in electrical contact between the enzyme and the mediating redox polymer. In the presence of glucose, the current generated due to the catalytic oxidation of glucose to gluconolactone is measured, and a response is obtained that is binding-dependent. The tethering of the probe DNA and redox polymer to the SAM improves the stability of the surface to assay conditions of rigorous washing and high salt concentration (1 M). These conditions eliminate nonspecific interaction of both the target DNA and the enzyme-avidin conjugate with the recognition surfaces. The sensor response increases linearly with increasing concentration of target DNA in the range of 1 x 10(-9) to 2 x 10(-6) M. The detection limit is approximately 1.4 fmol, (corresponding to 0.2 nM of target DNA). Regeneration of the recognition surface is possible by treatment with 0.25 M NaOH solution. After rehybridization of the regenerated surface with the target DNA sequence, >95% of the current is recovered, indicating that the redox polymer and probe DNA are strongly bound to the surface. These results demonstrate the utility of the proposed approach.

Avidin↗
PubMedDate not supplied

A polyethylene glycol copolymer for carrying and releasing multiple copies of cysteine-containing peptides.

Two different methods were developed to prepare an adduct of a poly(ethylene glycol)-lysine copolymer with either cysteamine or 1-amino-2-methyl-2-propanethiol. Cysteine-containing peptides could then be disulfide-linked to the thiol groups on the polymer in a facile manner. In the described procedures, a coupling ratio of about 8 peptides/molecule of poly(ethylene glycol)-lysine copolymer (Mw = 27 000) was typically attained. The products were stable at neutral pH, but the peptides could be released from the polymer in a physiologically relevant reducing environment. The release rate was highly dependent on the linker used for forming the disulfide bond. To illustrate the potential biomedical usefulness of this polymer carrier, a Tat peptide-PEG conjugate was shown to inhibit expression of a reporter gene fused to the TAR element of human immunodeficiency virus in a model cell assay.

Biotinylation↗
PubMedDate not supplied

Sulfur shuffle: modulating enzymatic activity by thiol-disulfide interchange.

The facile modulation of biological processes is an important goal of biological chemists. Here, a general strategy is presented for controlling the catalytic activity of an enzyme. This strategy is demonstrated with ribonuclease A (RNase A), which catalyzes the cleavage of RNA. The side-chain amino group of Lys41 donates a hydrogen bond to a nonbridging oxygen in the transition state for RNA cleavage. Replacing Lys41 with a cysteine residue is known to decrease the value of k(cat)/K(m) by 10(5)-fold. Forming a mixed disulfide between the side chain of Cys41 of K41C RNase A and cysteamine replaces the amino group and increases k(cat)/K(m) by 10(3)-fold. This enzyme, which contains a mixed disulfide, is readily deactivated by dithiothreitol. Forming a mixed disulfide between the side chain of Cys41 and mercaptopropyl phosphate, which is designed to place a phosphoryl group in the active site, decreases activity by an additional 25-fold. This enzyme, which also contains a mixed disulfide, is reactivated in the presence of dithiothreitol and inorganic phosphate (which displaces the pendant phosphoryl group from the active site). An analogous control mechanism could be installed into the active site of virtually any enzyme by replacing an essential residue with a cysteine and elaborating the side chain of that cysteine into appropriate mixed disulfides.

Binding Sites↗
PubMed1990

Aminophospholipid translocation in erythrocytes: evidence for the involvement of a specific transporter and an endofacial protein.

The transport of exogenously supplied fluorescent analogues of aminophospholipids from the outer to inner leaflet in red blood cells (RBC) is dependent upon the oxidative status of membrane sulfhydryls. Oxidation of a sulfhydryl on a 32-kDa membrane protein by pyridyldithioethylamine (PDA) has been previously shown [Connor & Schroit (1988) Biochemistry 27, 848-851] to inhibit the transport of NBD-labeled phosphatidylserine (NBD-PS). In the present study, other sulfhydryl oxidants were examined to determine whether additional sites are involved in the transport process. Our results show that diamide inhibits the transport of NBD-PS via a mechanism that is independent of the 32-kDa site. This is shown by the inability of diamide to block labeling of the 32-kDa sulfhydryl with 125I-labeled PDA and to protect against PDA-mediated inhibition of NBD-PS transport. diamide-mediated inhibition, but not PDA-mediated inhibition, could be reversed by reduction with cysteamine or endogenous glutathione. Similarly, treatment of RBC with 5,5'-dithiobis(2-nitrobenzoic acid), which depletes endogenous glutathione and induces oxidation of endofacial proteins [Reglinski et al. (1988) J. Biol. Chem. 263, 12360-12366], inhibited NBD-PS transport in a manner analogous to diamide. Once established, the asymmetric distribution of NBD-PS could not be altered by oxidation of either site. These data indicate that a second site critical to the transport of aminophospholipids resides on the endofacial surface and suggest that the transport of aminophospholipids across the bilayer membrane of RBC depends on a coordinated and complementary process between a cytoskeletal component and the 32-kDa membrane polypeptide; both must be operative for transport to proceed.

4-Chloro-7-nitrobenzofurazan↗
PubMed2005

Biochemical investigation of pikromycin biosynthesis employing native penta- and hexaketide chain elongation intermediates.

The unique ability of the pikromycin (Pik) polyketide synthase to generate 12- and 14-membered ring macrolactones presents an opportunity to explore the fundamental processes underlying polyketide synthesis, specifically the mechanistic details of chain extension, keto group processing, acyl chain release, and macrocyclization. We have synthesized the natural pentaketide and hexaketide chain elongation intermediates as N-acetyl cysteamine (NAC) thioesters and have used them as substrates for in vitro conversions with engineered PikAIII+TE and in combination with native PikAIII (module 5) and PikAIV (module 6) multifunctional proteins. This investigation demonstrates directly the remarkable ability of these monomodules to catalyze one or two chain extension reactions, keto group processing steps, acyl-ACP release, and cyclization to generate 10-deoxymethynolide and narbonolide. The results reveal the enormous preference of Pik monomodules for their natural polyketide substrates and provide an important comparative analysis with previous studies using unnatural diketide NAC thioester substrates.

Amino Acid Sequence↗
PubMed2005

Bifunctional small molecules are biomimetic catalysts for silica synthesis at neutral pH.

Silicatein is an enzyme isolated from the biosilica produced by the marine demosponge, Tethya aurantia. Once isolated from the sponge, silicatein can be used in vitro to catalyze the hydrolysis and direct polycondensation of a wide variety of alkoxide, ionic, and organometallic precursors to the corresponding chalcogens at standard temperature and pressure and neutral pH. On the basis of these results, an array of small molecules that mimic the unique physiochemical environment found in the enzyme active site was investigated for catalytic activity in the formation of silica from silicon alkoxides at neutral pH. The most successful of these biomimetic catalysts (cysteamine) was used to encapsulate firefly luciferase, green and blue fluorescent proteins (GFP, BFP), and Escherichia coli cells expressing GFP in silica matrixes. The benign conditions required for the catalysis of synthesis of these silica composites does not impair the activities of the encapsulated enzyme, fluorescent proteins, or live cells as shown by fluorescence measurements. In conjunction with microcontact printing, this biomimetically catalyzed encapsulation method has been used to produce patterned functional arrays of silica nanoparticulate composite materials.

Animals↗
PubMed2001

New flavanol derivatives from grape (Vitis vinifera) byproducts. Antioxidant aminoethylthio-flavan-3-ol conjugates from a polymeric waste fraction used as a source of flavanols.

A new family of antioxidants has been obtained from a residual fraction of polymeric polyphenols of grape origin. The integral exploitation of resources is important in any sustainable production scheme. Many byproducts and residues generated by the agroindustries contain polyphenols with potential application as preventative agents against cancer and cardiovascular diseases. Among these polyphenols oligomeric proanthocyanidins are particularly significant. The polymeric forms, considered of less interest because of their astringent properties, constitute the largest portion of the biologically active plant proanthocyanidins. The new compounds described here result from the breakdown of polymeric flavanols in the presence of cysteamine and bear an amino function, which facilitates their isolation from complex mixtures by cation-exchange gels or resins. In this way, valuable antioxidant molecules can be efficiently obtained from otherwise wasted polymers. The new molecules appear to be as effective as their underivatized counterparts (flavan-3-ols) as antioxidants.

Antioxidants↗
PubMed2002

Generation of roasted notes based on 2-acetyl-2-thiazoline and its precursor, 2-(1-hydroxyethyl)-4,5-dihydrothiazole, by combined bio and thermal approaches.

Roasted notes contribute to the flavor of thermally processed foods such as meat and bread. 2-Acetyl-2-thiazoline is one of the key volatile compounds responsible for the roasted and popcorn-like aroma character. We report here on the biogeneration of flavoring preparations with intense roasted notes, which are characterized by a high content of 2-acetyl-2-thiazoline. These flavoring preparations were obtained by fermentation of cysteamine, ethyl-L-lactate, and D-glucose with baker's yeast. The precursor of 2-acetyl-2-thiazoline, 2-(1-hydroxyethyl)-4,5-dihydrothiazole, was prepared under mild conditions by microbial reduction of the carbonyl group of 2-acetyl-2-thiazoline using baker's yeast as biocatalyst. The addition of 2-(1-hydroxyethyl)-4,5-dihydrothiazole as aroma precursor to pizza dough resulted in an increase of the roasted note.

Bread↗
PubMed2002

Structural determination and odor characterization of N-(2-mercaptoethyl)-1,3-thiazolidine, a new intense popcorn-like-smelling odorant.

The chemical structure of a novel, roasty, popcorn-like-smelling aroma compound formed from the reaction of fructose with cysteamine was studied by high-resolution mass spectrometry and nuclear magnetic resonance experiments. The structure of N-(2-mercaptoethyl)-1,3-thiazolidine exhibiting the extremely low odor threshold of 0.005 ng/L in air was finally confirmed by synthesis.

Cysteamine↗
PubMed1983

Relationship between metabolism and radioprotective activity of 2-phenylthiazolidine and its m-bromo derivative.

Molecular biotransformation of 2-phenylthiazolidine (1) and its m-bromo derivative (2) in the mouse is followed by autoradiographic studies and assessed by analysis of urinary metabolites. Cysteamine (4) is one of the metabolites of compounds 1 and 2. Radioprotective activity and efficacy over a period of time of 1, 2, and 4 correlate closely with distribution and metabolism.

Animals↗
PubMed2001

Thiazolidine prodrugs as protective agents against gamma-radiation-induced toxicity and mutagenesis in V79 cells.

Representatives of two classes of thiazolidine prodrug forms of the well-known radioprotective agents L-cysteine, cysteamine, and 2-[(aminopropyl)amino]ethanethiol (WR-1065) were synthesized by condensing the parent thiolamine with an appropriate carbonyl donor. Inherent toxicity of the prodrugs was assessed in V79 cells using a clonogenic survival assay. Protection against radiation-induced cell death was measured similarly after exposure to 0--8 Gy gamma ((137)Cs) radiation. Antimutagenic activity was determined at the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) locus. All thiazolidine prodrugs exhibited less toxicity than their parent thiolamines, sometimes dramatically so. Protection against radiation-induced cell death was observed for the 2-alkylthiazolidine, 2(R,S)-D-ribo-(1',2',3',4'-tetrahydroxybutyl)thiazolidine (RibCyst), which produced a protection factor at 8 Gy of 1.8; the cysteine analogue, 2(R,S)-D-ribo-(1',2',3',4'-tetrahydroxybutyl)thiazolidine-4(R)-carboxylic acid (RibCys), was less active. RibCyst also exhibited excellent antimutational activity, rivaling that of WR-1065. The 2-oxothiazolidine analogues showed little activity in either determination under the conditions tested, perhaps due to their enhanced chemical and biochemical stability.

Animals↗
PubMed2002

Immobilization of aminothiols on poly(oxyalkylene phosphates). Formation of poly(oxyethylene phosphates)/cysteamine complexes and their radioprotective efficiency.

The necessity to apply near-toxic amounts of radioprotective drugs to achieve adequate protection during radiation treatments represents a major problem in human medicine. One of the promising strategies to suppress the toxicity of these drugs involves their incorporation into biocompatible polymers. In this study cysteamine (Cy) was attached to poly(oxyethylene phosphate), POEP, via an ionic bond. Radioprotection of E. coli B cells by this substance and its acute toxicity on male C57 BL mice were measured. The toxicity of Cy immobilized within the poly(oxyethylene phosphate) was significantly lower in comparison to pure Cy while its radioprotective efficiency remained high at half the maximum tolerable dose. The high radioprotective efficiency of the Cy/POEP complexes was further confirmed on mice at different polymer molecular weight characteristics, drug immobilization degrees, application times, and doses. It was found that POEP with molecular weight 4700 Da and containing 24% repeating units with attached Cy has the highest protection potential combined with a depot effect.

Animals↗
PubMed2001

Chemoenzymatic synthesis of neoglycopeptides: application to an alpha-Gal-terminated neoglycopeptide.

A novel methodology for the enzymatic preparation from suitably derivatized oligosaccharides of N-linked neoglycopeptides using the microbial glutaminyl-peptide gamma-glutamyl transferase, transglutaminase (TGase), is described. N-Allyl glycosides of various oligosaccharides were photochemically coupled with cysteamine to yield amino-terminated thioether spacers, which were accepted by transglutaminase to transamidate the side-chain gamma-carboxamide group in the dipeptide Z-Gln-Gly.

Acylation↗
PubMed2005

Electrostatic and covalent interactions in CdTe nanocrystalline assemblies.

This paper focuses on the interactions between cysteamine-stabilized CdTe nanocrystals [CdTe(CA) NCs] and thioglycolic-acid-stabilized CdTe nanocrystals [CdTe(TGA) NCs]. These interactions were examined by the absorption, continuous, and time-resolved photoluminescence (PL) spectra of the electrostatically mixed and the covalently linked NCs assemblies comprised of the oppositely surface charged CdTe(CA) and CdTe(TGA) NCs and by a comparison with those of the corresponding pristine NCs. The CdTe(CA)-CdTe(TGA) coupling is dictated by the surfactant spacer, ranging between 0.93 and 1.14 nm and by electrostatic and covalent interactions, enabling a Förster resonance energy transfer (FRET) process among the NCs. The results revealed an excellent spectral overlap between the emission of the CdTe(TGA) NCs and the absorption of the CdTe(CA) NCs as well as a PL spectral red shift on the formation of electrostatic and covalent interactions. Furthermore, the measurements showed a lifetime ranging between 1.2 and 3 ns for the electrostatically mixed and the covalently linked assemblies, shorter than those of the pristine CdTe(CA) NCs and CdTe(TGA) NCs, both of which measured as approximately 5.5 ns. When CdTe(TGA) NCs performed as the most efficient donors, FRET rates of 10(10)-10(11) s(-1) were calculated for the electrostatically mixed NCs or covalently linked NCs.

Cadmium↗
PubMed2004

Improving neuron-to-electrode surface attachment via alkanethiol self-assembly: an alternating current impedance study.

In this work, the omega-amine alkanethiols, cysteamine (CA) and 11-amino-1-undecanethiol (11-AUT), were chemisorbed as self-assembled monolayers (SAMs) onto 250-microm gold microelectrodes that were microlithographically fabricated within eight-well cell culture plates and investigated as a means to improve neuron-to-electrode surface attachment (NESA). Dynamic contact angle (DCA) measurements showed similar advancing, theta(a) (69 degrees and 65 degrees ), but contrasting receding contact angles, theta(r) (9 and 30 degrees ) for CA- and 11-AUT-SAMs, respectively. The corresponding hysteresis (Deltatheta(ar) = 60 and 35 degrees, respectively) indicates the CA-SAM displays greater amphiphilic character than the 11-AUT-SAM. A portion of the greater Deltatheta(ar) for CA-SAMs may arise from surface heterogeneity, as compared to sputter-deposited gold and 11-AUT-SAMs. Tapping mode atomic force microscopy (AFM) confirmed a 6% increase (CA-SAM) and a 22% decrease (11-AUT-SAM) in surface roughness when compared to clean but unmodified, sputter-deposited gold. The extracellular matrix cell adhesion proteins, collagen, fibronectin, and laminin, were covalently coupled to the aminoalkanethiol-decorated gold electrodes via acid-amine heterobifunctional cross-linking. Using fluorescein isothiocyanate-tagged laminin, confocal fluorescence microscopy of both CA- and 11-AUT-SAM-modified and unmodified gold microelectrodes confirmed coupling of the protein to the electrode and was readily distinguishable from nonspecifically adsorbed protein. DCA measurements of laminin physisorbed directly onto gold or covalently immobilized via CA- or 11-AUT-SAM had similar advancing (ca. 63-65 degrees ) and receding (ca. 7-9 degrees ) contact angles. Tapping mode AFM of these protein-bearing surfaces likewise showed dimerized protein aggregates of similar surface roughness. PC-12 cells cultured to confluence on both unmodified and SAM-modified, protein-derivatized gold microelectrodes were examined by alternating current impedance (50 mV p-t-p at 4 kHz). CA- and 11-AUT-SAM-modified surfaces when serving as a foundation or covalently immobilized adhesion proteins produced highly stable and reproducible temporal impedance responses. On the basis of the magnitude and the reproducibility of the impedance responses, the CA-SAM-modified surfaces were identified as being best suited for optimal neuron-to-electrode contact with laminin. Laminin performed best when compared to collagen and fibronectin. Covalent immobilization of the adhesion-promoting proteins results in enhanced NESA by tightly anchoring cells to the electrode.

Adsorption↗
PubMed2005

Electrochemical impedance spectroscopy of polyelectrolyte multilayer modified gold electrodes: influence of supporting electrolyte and temperature.

Electrochemical impedance spectroscopy and cyclic voltammetry are employed to characterize poly(styrenesulfonate)/poly(allylamine hydrochloride) multilayers assembled onto cysteamine-modified gold surfaces. The influence of the supporting electrolyte and temperature on the impedance response is studied because of both its practical interest and the need to test further the capillary membrane model recently developed by Barreira et al. [J. Phys. Chem. B 2004, 108, 17973]. The results obtained are interpreted quite satisfactorily in terms of this model, thus providing additional support to its usefulness for the description of ionic transport through polyelectrolyte multilayers. It is observed that the nature of the supporting electrolyte affects the film resistance and the electrode coverage. The temperature dependence of the diffusion coefficient is shown to follow the Arrhenius law, and the activation energy is estimated as 61 kJ/mol. Experiments with a large number of layers are also included to show that the impedance response of the multilayer then resembles that of a homogeneous membrane.

Biosensing Techniques↗
PubMed2003

Thiyl radical reaction with thymine: absolute rate constant for hydrogen abstraction and comparison to benzylic C-H bonds.

Free radical damage of DNA is a well-known process affecting biological tissue under conditions of oxidative stress. Thiols can repair DNA-derived radicals. However, the product thiyl radicals may also cause biological damage. To obtain quantitative information on the potential reactivity with DNA components, we measured the rate constant for hydrogen abstraction by cysteamine thiyl radicals from thymine C5-CH(3), k = (1.2 +/- 0.8) x 10(4) M(-1) s(-1), and thymidine-5'-monophosphate, k = (0.9 +/- 0.6) x 10(4) M(-1) s(-1). Hence, the hydrogen abstraction from C5-CH(3) occurs with rate constants similar to the hydrogen abstraction from the carbohydrate moieties. Especially at low oxygen concentration such as that found in skeletal muscle, such hydrogen abstraction processes by thiyl radicals may well compete against other dioxygen-dependent reactions. The rate constants for hydrogen abstraction at thymine C5-CH(3) were compared to those with benzylic substrates, toluenesulfonic acid, and benzyl alcohol.

Amidines↗
PubMed2002

Role of heme oxygenase-1 in the biogenesis of corpora amylacea.

Corpora amylacea (CA) are glycoproteinaceous inclusions that accumulate in the human brain during normal aging and to a greater extent in Alzheimer's disease. We previously demonstrated that, in cultured rat astroglia, cysteamine (CSH) upregulates heme oxygenase-1 (HO-1) and promotes the transformation of normal mitochondria into CA-like inclusions. In the current study, primary cultures of neonatal rat astroglia were exposed to 880 micro M CSH for three months in the presence or absence of dexamethasone, a suppressor of HO-1 gene transcription. Cells were double-labeled with periodic acid-Schiff reagent (PAS) and antisera against ubiquitin, HO-1, or a mitochondrial epitope. CA were quantified and their immunostaining characteristics analyzed using confocal microscopy. HO-1 immunofluorescence was more abundant in cultures exposed to CSH alone relative to untreated control cultures and cultures exposed to both CSH and dexamethasone. Mature CA appeared as large (5-50 microM), spherical or polygonal, intensely PAS-positive inclusions within glial cytoplasm or deposited extracellularly. The inclusions manifested intense rim and, less commonly, homogeneous or stippled patterns of immunoreactivity for ubiquitin, HO-1, and the mitochondrial marker. Monolayers exposed to CSH exhibited 660% more CA relative to untreated controls (P < 0.05). Numbers of CA in cultures exposed to CSH were diminished by co-administration of 50 microg/ml dexamethasone (P < 0.05 relative to CSH alone) or 100 microg/ml dexamethasone (P < 0.05 relative to CSH alone). Numbers of CA in cultures co-treated with CSH and 50 microg/ml dexamethasone or 100 microg/ml dexamethasone were not significantly different from untreated control values. Up-regulation of HO-1 may contribute to the formation of CA in aging astroglia.

Animals↗