title: Homogeneous substrate-labeled fluorescent immunoassay for theophylline in serum.
abstract: A substrate-labeled fluorescent immunoassay for theophylline in serum is described. 8-(3-Aminopropyl)-theophylline is covalently attached to a fluorogenic enzyme substrate, 7-beta-galactosylcoumarin-3-carboxylic acid. Hydrolysis of this theophylline-labeled substrate by beta-galactosidase yields a fluorescent product. When antibody to theophylline interacts with this substrate, the resulting complex is inactive as an enzyme substrate. For measuring theophylline, competitive protein-binding reactions are set up, with the theophylline in the sample competing with the substrate for the antibody-binding sites. The substrate not bound to antibody is hydrolyzed by beta-galactosidase, producing fluorescence that is proportional to the theophylline concentration. Results for theophylline determined by this method in clinical samples of serum correlated well (r > 0.96) with results obtained by gas-chromatographic or enzyme immunoassay procedures. The within-run CV for three control samples ranged from 1.1 to 2.8%, the between-run CB from 2.3 to 4.5%.
mesh_terms: D000918:Antibody Specificity; D005453:Fluorescence; D005696:Galactosidases; D006801:Humans; D006868:Hydrolysis; D007118:Immunoassay / Q000379:methods*; D013806:Theophylline / Q000097:blood* / Q000276:immunology
chemical_list: D013806:Theophylline; D005696:Galactosidases