Low-level chemiluminescence of N-beta-alanyl-L-histidine (L-carnosine)

ZstatFlu-II test: a chemiluminescent neuraminidase assay for influenza viral diagnostics

The ZstatFlu-II test is a highly sensitive, specific, rapid, point-of-care chemiluminescent diagnostic test for influenza infection. Influenza viral neuraminidase-specific substrate, spiroadamantyl-1,2-dioxetane-4,7-dimethoxy-N-acetyl-neuraminic acid, is at the core of the ZstatFlu-II Test. The enzymatic reaction was carried out at 25 degrees C and neutral pH, representing the optimum assay conditions for influenza types A and B viral neuraminidases. The results were outputted on a Polaroid trade mark High Speed Detector Film. Positive results appeared as a '+'-shaped white film image; negative results produced no image. The 'glow' kinetics, facilitated by a unique combination of light enhancers, also 'tuned' the wavelength of emission to match the spectral properties of the film. The substrate hydrolysed non-enzymatically at acid pH or at temperatures above 25 degrees C. In order to minimize false positives, the ZstatFlu-II Test was formatted with 0.3-0.4 K(m) substrate and freezing the test kit until use. The pH optimization of the ZstatFlu-II test is discussed with reference to model compounds of sialyl-glycosides. A nucleophilic attack or an electrostatic stabilization of a developing carbonium ion under the influence of the adjacent carboxyl group was probably responsible for non-enzymatic hydrolysis of the substrate. Intramolecular general acid catalysis is proposed as a mechanism for the lability of the O-glycosidic linkage of the substrate.

Thiols enhance the sensitivity of luminescent assays for non-cross-linked and covalently cross-linked aminophthalhydrazides

Transglutaminases catalyse an acyl-transfer reaction between the gamma-carboxamide of a protein or peptide-bound glutamine (P-CH2-gammaCH2-CO-1NH2) and the primary amino group of mono- or polyamines (R-2NH2), covalently cross-linking the reactants by an isopeptide bond: P-CH2-gammaCH2-CO-1NH2 + R-2NH2 --> P-CH2-gammaCH2-CO-2NH-R + 1NH3. We reported that N-(4-aminobutyl)-N-ethylisoluminol (ABEI) was a chemiluminescent (CL) amine substrate for transglutaminases. We now identified N-(6-aminohexyl)-N-ethylisoluminol (AHEI) as a second, less reactive, transglutaminase substrate. A structure-based explanation is offered for the lower reactivity of AHEI. Optimum CL from non-cross-linked or cross-linked ABEI or AHEI was elicited in the presence of 10 mmol/L dithiothreitol, by oxidizing with a mixture of 20 mmol/L potassium ferricyanide and 10 mmol/L hydrogen peroxide in 100 mmol/L NaOH. The limits of detection and quantitation for non-cross-linked aminophthalhydrazides obtained in this system were: 20 fmol and 60 fmol for ABEI and 10 fmol and 30 fmol for AHEI. These values represented a 500-800-fold improved sensitivity. Delayed peak CL and CL decay in the presence of dithiothreitol contributed to improving the sensitivity. The data could be useful for improving the immunoassays for aminophthalhydrazides and facilitate the development of high throughput assays for transglutaminases.