Detection of esterase activity by chromogenic and fluorogenic probe based on an O-nitrobenzoxadiazole (O-NBD) unit

We designed a conjugated molecule bearing an O-nitrobenzoxadiazole (O-NBD) unit and an acetylated trimethyl lock as a chromogenic and fluorogenic probe for the detection of esterase activity. The designed molecule was briefly synthesized from a commercially available compound in two steps. Several experiments revealed that the conjugated molecule serves as a sensitive chromogenic and fluorogenic probe for the detection of porcine liver esterase activity. Mechanistic studies indicated that an intramolecular O- to N-NBD migration is involved in the chromogenic/fluorogenic phenomena. The results here would be helpful for designing other O-NBD-based chromogenic/fluorogenic probes in future.     

Novel type of general protein assay using a chromogenic and fluorogenic amine-reactive probe

We report on a new and simple one-reagent method for general protein assay. It makes use of one of two new reactive labeling reagents presented here (and referred to as pyrylium [Py] labels). These can be applied for both photometric and fluorometric protein assays at near neutral pHs at room temperature. The Py labels undergo a large spectral change on conjugation to the amino group of proteins and typically change their color from blue to red. Therefore, and unlike in other assays, there is no need to separate the unconjugated (blue) label from the red conjugate, which can be determined by direct photometry with a limit of detection of 1.2 microg/ml for human serum albumin. The assay can be extended to fluorometry because the fluorescence of the free Py label is weak (with a quantum yield of <1%) but increases strongly (to >40%) on conjugation. The strong fluorescence of the red conjugates can be determined directly and without interference by the blue (and weakly fluorescent) free label. The fluorometric assay resulted in a limit of detection of 60 ng/ml for bovine serum albumin (BSA). Validation of the fluorescence assay of blood plasma samples spiked with BSA gave recoveries in the range from 91 to 103%.     

New fluorogenic substrate for esterase activity of alpha-chymotrypsin and related enzymes

A new fluorogenic substrate, benzyloxycarbonyl-L-phenylalanine 4-methylcoumaryl-7-ester, has been developed for determination of the esterase activity of alpha-chymotrypsin and related enzymes. Synthesis of the substrate was achieved simply by the carbodiimide condensation of benzyloxycarbonyl-L-phenylalanine and 7-hydroxy-4-methylcoumarin in a 86% yield. The esterase activity was measured by increase of the fluorescence intensity at excitation and emission wavelengths of 325 and 465 nm, respectively. An initial rate of hydrolysis was linear over a 100-fold range of the enzyme concentration. As little as 2 ng of alpha-chymotrypsin could be detected in the standard assay. A typical enzyme assay, stability of the substrate, kinetic parameters, and specific activity have been reported.     

Label-free G-quadruplex-specific fluorescent probe for sensitive detection of copper(II) ion

An effective G-quadruplex-based probe has been constructed for rapid and sensitive detection of Cu(2+). In this probe, an anionic porphyrin, protoporphyrin IX (PPIX) served as a reference signal, which binds to G-quadruplex specifically and the fluorescence intensity increases sharply. While, in the presence of Cu(2+), the G-quadruplex can catalyze the related Cu(2+) insertion into the protoporphyrin, the fluorescent intensity is decreased. The fluorescence of the response ligand could be selectively quenched in the presence of Cu(2+) and not interfered by other metal ions. The probe provided an effective platform for reliable detection of Cu(2+) with a detection limit as low as 3.0nM, the high sensitivity was attributed to the strong metalation of PPIX with Cu(2+) catalyzed by G-quadruplex (PS5.M). Linear correlations were obtained over the logarithm of copper ion concentration in the range from 8×10(-9)M to 2×10(-6)M (R=0.998). The G-quadruplex-based probe also could be used to detect Cu(2+) in real water samples. Additionally, these striking properties endow the G-quadruplex-ligand with a great promise for analytical applications.     

Evaluation of the use of chromogenic and fluorogenic substrates in solid-phase enzyme linked immunosorbent assays (ELISA)

Fluorogenic and chromogenic substrates were used in direct and trapping enzyme-linked immunosorbent assays (ELISA) for the detection of mouse IgG and foot-and-mouth disease virus (FMDV). The detection limits for both antigens were compared using different combinations of enzymes and substrates. Various times and concentrations of chemicals were used to obtain maximum sensitivity for both systems. Similar sensitivities were found using fluorogenic and chromogenic substrates. Tetramethyl benzidine substrate for horse-radish peroxidase enzyme conjugates was found to attain the highest sensitivity levels for chromogenic assays (0.12 ng IgG/ml and 1.0 ng/ml FMDV respectively), after 10 min incubation. Of the two fluorogenic enzyme/substrates studied, B-galactosidase was the most sensitive but required extended incubation times (2-3 h) as compared with chromogenic systems. Special microplates for fluoro-immunoassay (FIA) were compared with conventional microplates and no advantage was found to justify their use. An alkaline phosphatase anti-guinea-pig conjugate was used to confirm the equivalence of fluorogenic and chromogenic substrates in terms of sensitivity. A comparison of the amount of signal generated using various concentrations of enzyme in the absence of antigen was made for two different alkaline phosphatase conjugates to obtain theoretical sensitivity limits. One possible advantage of fluorogenic substrates is that high binding ratio can improve the confidence in discrimination of positive results.     

Determination of catalase activity using chromogenic probe involving iso-nicotinicacidhydrazide and pyrocatechol

A biocatalatic pathway involving chromogenic probe has been proposed for the determination of catalase activity by means of iso-nicotinicacidhydrazide (INH) and pyrocatechol (PC). The assay is based on the enzymatic consumption of hydrogen peroxide using INH-PC system. The response of the catalase activity was ascertained by the rate of the reaction involving 14.10 mM H₂O₂. On addition of H₂O₂, INH-PC indicator system formed a chromogenic product with absorbance maxima at 490 nm. Hence the activity of catalase was directly measured by the chromogenic response in the formation of the coupled product. The catalase assay was elaborated by the kinetic response of the INH-PC system. The linearity of the catalase activity and H₂O₂ was in the range 0.2-7.0 units and 1.76-7.0 mM, respectively in 3 ml solution. The catalytic efficiency and catalytic power were calculated. The Michaelis-Menten constant of INH, PC and H₂O₂ were found to be 0.344, 0.176 and 8.82 mM, respectively. The indicator reaction was applied in the determination of catalase activity in mycelia mats and culture media.     

A highly sensitive fluorogenic probe for cytochrome P450 activity in live cells

A derivative of rhodamine 110 has been designed and assessed as a probe for cytochrome P450 activity. This probe is the first to utilize a 'trimethyl lock' that is triggered by cleavage of an ether bond. In vitro, fluorescence was manifested by the CYP1A1 isozyme with k(cat)/K(M)=8.8x10(3)M(-1)s(-1) and K(M)=0.09microM. In cellulo, the probe revealed the induction of cytochrome P450 activity by the carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin, and its repression by the chemoprotectant resveratrol.     

Cobalt (3) carboxypeptidase A: preparation and esterase activity

Co(II) carboxypeptidase A has been oxidized to Co(III) carboxypeptidase A with hydrogen peroxide. The resultant metalloprotein has an absorption spectrum different from that of the Co(II) enzyme and the metal is no longer removable by dialysis. The Co(III) carboxypeptidase A retains esterase activity comparable to that of the Co(II) enzyme and has very low peptidase activity. This demonstrates that scission of a bond to the first coordination sphere of the metal is not necessary for the hydrolysis of ester substrates.     

Anticandidal activity of hetero-dinuclear copper(II) Mn(II) Schiff base and its potential action of the mechanism

Invasive fungal infections are one of the major challenges especially for immunosuppressed patients since they are drug resistant and pathogen to patients. Therefore, developing new, efficient and nonresistant antifungal agents have been a primary focus of international research. In the current study, a novel Schiff base [hetero-dinuclear copper(II) Mn(II) complex] (SB) derivative was investigated for its anticandidal activity against Candida albicans and possible mechanisms inducing cell death. The results revealed that SB treatment induces apoptotic and necrotic pathways in C. albicans ATCC10231 strain. Intracellular reactive oxygen species production determined by 2′,7′-dichlorofluorescein diacetate staining was triggered by SB and amphotericin B administrations in a dose-dependent manner. Gene expression analysis demonstrated that SB exposure resulted in regulation of critical development and stress related gene expressions. SB treatment directly upregulated expression of stress related genes, DDR48 and RIM101, while suppressed important cell signaling and antibiotic resistance acquiring related genes such as HSP90, ERG11 and EFG1. Furthermore, CaMCA1 mRNA levels were found to be significantly high in SB-treated yeast cells, indicating possible caspase-like mechanism activation. Scanning electron microscopy analysis confirmed that SB treatment led to severe cell wall integrity disruption and wrinkling. The study will encourage development of SB-based anticandidal regimens but further studies are highly warranted to understand limitations and the extended use in the routine.     

Inhibition of proteinase K activity by copper(II) ions

Disease-related prion protein, PrPSc, can be distinguished from its normal cellular precursor, PrPC, by its detergent insolubility and partial resistance to proteolysis. Several studies have suggested that copper(II) ions can convert PrPC to a proteinase K-resistant conformation; however, interpretation of these studies is complicated by potential inhibition of proteinase K (PK) by copper(II) ions. Here we have examined directly the kinetic and equilibrium effects of copper(II) ions on PK activity using a simple synthetic substrate, p-nitrophenyl acetate. We show that at equilibrium two to three copper(II) ions bind stoichiometrically to PK and destroy its activity (Kd < 1 microM). This inhibition has two components, an initial reversible and weak binding phase and a slower, irreversible abolition of activity with a half-time of 6 min at saturating copper(II) ion concentrations. Copper(II) ions produce a similar biphasic inhibition of PK activity in the presence of brain homogenate but only when the copper(II) ion concentration exceeds that of the chelating components present in brain tissue. Under these conditions, the apparent resistance of PrPC to proteolysis by PK appears to be directly attributable to the inhibition of PK activity by copper(II) ions.     

Elongation factor (EF-Tu) gene probe detects polymorphism in Mycoplasma strains

Abstract Polymorphism in mycoplasma strains was observed by Southern blot hybridization of the digested mycoplasma DNAs with the elongation factor (EF-Tu) gene tuf of Escherichia coli . The hybridization patterns revealed genotypic heterogeneity among Mycoplasma gallisepticum strains and a remarkable degree of homogeneity among Mucoplasma pneumoniae strains isolated from pneumonia patients. The distinction among M. gallisepticum strain clusters achieved by the tuf gene probe corresponded exactly with that obtained with the rRNA gene probe pMC5. The tuf gene probe may thus be added as another effective tool in the taxonomy of Mollicutes and in epidemiological surveys of mycoplasma infections.     

Total antioxidant capacity assay of human serum using copper(II)-neocuproine as chromogenic oxidant: the CUPRAC method

BACKGROUND: Tests measuring the combined antioxidant effect of the nonenzymatic defenses in biological fluids may be useful in providing an index of the organism's capability to counteract reactive species known as prooxidants, resist oxidative damage and combat oxidative stress-related diseases. The selected chromogenic redox reagent for the assay of human serum should be easily accessible, stable, selective, respond to all types of biologically important antioxidants such as ascorbic acid, alpha-tocopherol, beta-carotene, reduced glutathione (GSH), uric acid and bilirubin, regardless of chemical type or hydrophilicity. Currently, there is no rapid method for total antioxidant assay of human serum meeting the above criteria.METHODS: Our recently developed cupric reducing antioxidant capacity (CUPRAC) spectrophotometric method for a number of polyphenols and flavonoids using the copper(II)-neocuproine reagent in ammonium acetate buffer was now applied to a complete series of plasma antioxidants for the assay of total antioxidant capacity (TAC) of serum, and the resulting absorbance at 450 nm was recorded either directly (e.g. for ascorbic acid, alpha-tocopherol and glutathione) or after incubation at 50 degrees C for 20 min (e.g. for uric acid, bilirubin and albumin), quantitation being made by means of a calibration curve. The lipophilic antioxidants, alpha-tocopherol and beta-carotene, were assayed in dichloromethane (DCM). Lipophilic antioxidants of serum were extracted with n-hexane from an ethanolic solution of serum subjected to centrifugation. Hydrophilic antioxidants of serum were assayed after perchloric acid precipitation of proteins in the centrifugate.Results: The molar absorptivities, linear ranges and trolox equivalent antioxidant capacity (TEAC) coefficients of the serum antioxidants were established with respect to the CUPRAC spectrophotometric method, and the results (TEAC, or TEAC coefficients) were evaluated in comparison to the findings of the ABTS/TEAC reference method using persulfate as oxidant. As for hydrophilic phase, a linear correlation existed between the CUPRAC and ABTS findings (r=0.58), contrary to current literature reporting that either serum ORAC or serum ferric reducing antioxidant potency (FRAP) does not correlate at all with serum TEAC. The analytical responses of serum antioxidants were shown to be additive, enabling a TAC assay. The intra- and inter-assay CVs were 0.7 and 1.5%, respectively, for serum.Conclusions: The CUPRAC assay proved to be efficient for glutathione and thiol-type antioxidants, for which the FRAP test was nonresponsive. The findings of CUPRAC completely agreed with those of ABTS-persulfate for lipophilic phase. The additivity of absorbances of all the tested antioxidants confirmed that antioxidants in the CUPRAC test did not chemically interact among each other so as to cause an intensification or quenching of the theoretically expected absorbance. As a distinct advantage over other electron-transfer based assays (e.g. Folin, FRAP, ABTS, DPPH), CUPRAC is superior in regard to its realistic pH close to the physiological pH, favourable redox potential, accessibility and stability of reagents and applicability to lipophilic antioxidants as well as hydrophilic ones.     

Metalloantibiotics: synthesis and antibacterial activity of cobalt(II), copper(II), nickel(II) and zinc(II) complexes of kefzol

Kefzol (kzl), a beta-lactam antibiotic, possesses various donor sites for interaction with transition metal(II) ions [Co(II), Cu(II), Ni(II) and Zn(II)] to form complexes of the type [M(kzl)2]Cl2 and [M(kzl)Cl], with molar ratio of metal: ligand (M:L) of 1:2 and 1:1 respectively. These complexes were prepared and characterized by physicochemical and spectroscopic methods. Their IR and NMR spectra suggest that kefzol potentially acts as a bidentate, tridentate as well as monoanionic tetradentate ligand. The complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis. The metal complexes were found to be more potent against one or more bacterial species than the uncomplexed kefzol.     

A homogeneous assay of kinase activity that detects phosphopeptide using fluorescence polarization and zinc

Homogeneous antibody-free assays of protein kinase activity have great utility in high-throughput screening in support of drug discovery. In an effort to develop such an assay, we have used a pair of fluorescein-labeled peptides of identical amino acid sequence with and without phosphorylation on serine to mimic the substrate and product, respectively, of a kinase. Using fluorescence polarization (FP), we have demonstrated that a mixture of zinc sulfate, phosphate-buffered saline, and bovine serum albumin added to the peptides dramatically and differentially increased the fluorescence polarization of the phosphorylated peptide over its nonphosphorylated derivative. A similar FP differential was observed using different peptide pairs, though the magnitude varied. The FP values obtained using this method were directly proportional to the fraction of phosphopeptide present. Therefore, an FP assay was developed using a proprietary kinase. Using this FP method, linear reaction kinetics were obtained in enzyme titration and reaction time course experiments. The IC(50) values for a panel of inhibitors of kinase activity were determined using this FP method and a scintillation proximity assay. The IC(50) values were comparable between the two methods, suggesting that the zinc FP assay may be useful as an inexpensive high-throughput assay for identifying inhibitors of kinase activity.     

Mutagenic activity of copper(II) chromate and dichromate complexes with polypyridines

Copper(II) chromate and dichromate complexes with 2,2'-bipyridyl and 1,10-phenathroline were tested for their mutagenic activity in the standard Ames test. All of six tested complexes exhibited markedly lower mutagenic activity than the reference compounds--potassium dichromate and sodium chromate. The blockage of Cr(VI) reduction capability in the presence of the complex Cu2+ ion and the competition between copper and chromium ions in the interaction with cellular components are discussed in the light of the results of our previous chemical study.     

Self-activating nuclease activity of copper (II) complexes of hydroxyl-rich ligands

Copper (II) complexes of Schiff bases derived from [1+1] condensation of salicylaldehyde, 2,3-dihydroxybenzaldehyde and 2,3,4-trihydroxybenzaldehyde with anthranilic acid (L1-L3) have been synthesized and characterized by elemental analyses, IR, UV-Vis spectra, room temperature magnetic susceptibility, electron paramagnetic resonance spectroscopy and cyclic voltammetry. The X-ray structure of [CuL1]n has been solved and refined to R = 0.0314. The crystals are monoclinic with space group P2(1) with cell constants a = 9.6820(13), b = 7.1446(11), c = 9.9315(13) A, beta = 98.385(8) degrees, Z = 2. The copper (II) ions are in a distorted tetrahedral environment sequentially bridged by carboxylate groups in the syn-anti conformation giving rise to a helix-like chain. The copper complexes with the inherent redox active hydroquinone functionality cleave plasmid pBR322 DNA without exogenous agents by a self-activating mechanism.     

Isoniazid-related copper(II) and nickel(II) complexes with antimycobacterial in vitro activity. Part 9

Isonicotinoylhydrazones 1, obtained by the primary antituberculous agent Isoniazid, have been used as monoanionic ligands (L) to prepare copper(II) 2 and nickel(II) 3 octahedral complexes of stoichiometry [MeL2(H2O)2]. Their antimycobacterial in vitro activity was evaluated against Mycobacterium tuberculosis H37Rv in comparison with the ligands. Complexes 2a, 2b, 2f, 3b, 3d and 3g displayed MIC values < or = 0.2 microg/mL.     

Synthesis, structure and biological activity of cobalt(II) and copper(II) complexes of valine-derived schiff bases

We have synthesized two cobalt(II) 2 and copper(II) 3 complexes of valine-derived Schiff bases. The obtained complexes were characterized by elemental analysis, FT-IR and X-ray diffraction. Biological studies of complexes 2 and 3 had been carried out in vitro for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi. Compound 3 was proven to be a broad spectrum agent, showed a significant inhibition of the growth of Gram-positive bacteria (Staphylococcus aureus, methicillin-resistant S. aureus, Bacillus subtilis, Micrococcus luteus), and pathogenic fungi (Candida spp., Cryptococcus neoformans, Rhodothece glutinis, Saccharomyces cerevisia, Aspergillus spp., Rhizopus nigricans) tested and a moderate activity against Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris and Enterobacter aerogenes) tested. The in vitro cytotoxicity of compound 3 was evaluated using hemolytic assay, in which the compound 3 was found to be non-toxic to human erythrocytes even at a concentration of 500mug/mL.     

Synthesis and characterization of a diruthenium-ibuprofenato complex comparing its anti-inflammatory activity with that of a copper(II)-ibuprofenato complex

The ibuprofen complex of diruthenium(II,III) was prepared and characterized by electronic (UV-Vis) and vibrational (FTIR) spectroscopies and thermogravimetry. The copper(II)-ibuprofenato complex was prepared by a different route from that described in the literature. Both complexes were tested in vivo for anti-inflammatory activity. Oral administration of the two complexes inhibited development of carrageenin-induced edema in rats, this inhibition being similar to that observed for oral administration of the parent drug (free ibuprofen). However, gastric irritation was lower as compared to that of ibuprofen. Diruthenium-ibuprofenato exhibited a protective effect at light intensity ulceration while the copper-ibuprofenato complex was more effective in the protection of severe intensity ulceration.