Homogeneous enzyme immunoassays

Homogeneous electrochemical enzyme immunoassays for both phenytoin and digoxin have been developed. In both cases the label was glucose-6-phosphate dehydrogenase, which catalyzes the reduction of NAD to NADH. The NADH produced was detected by LCEC at a carbon paste electrode. 

A homogeneous electrochemical enzyme immunoassay for 2,4-dinitrophenol-aminocaproic acid (DNP-ACA), has been developed based on antibody inhibition of enzyme conversion from the apo- to the holo- form Apoglucose oxidase was used as the enzyme label. This enzyme is inactive until binding of flavin adenine dinucleotide (FAD) to form the holoenzyme which is active. Hydrogen peroxide is the enzymatic product which is detected electrochemically. Because antibody bound apoenzyme cannot bind FAD, the production of HjOj is a measure of the concentration of free DNP-ACA in the sample. 

Rubenstein, J.L. Schneider, R. and Ullman, E. Homogenous enzyme immunoassay. Biochem Biophvs Res Commun 47 846, 1972. 

Koup, J.R. and Brodsky, B., Comparison of homogeneous enzyme immunoassay and high pressure liquid chromatography for the determination of theophylline concentration in serum, Am. Rev. Respir. Dis., 117,1135,1978. 

T. Fonong and G.A. Rechnitz, Homogeneous potentiometric enzyme immunoassay for human immunoglobulin G. Anal. Chem. 56, 2586-2590 (1984). 

Pankey, S. et al. 1986. Quantitative homogeneous enzyme immunoassays for amitriptyline, nortriptyline, imipramine, and desipramine. Clin Chem. 32 768. 

ELISA s (54, 55) are one of the most commonly used immunoassays in the food industry for detection of a wide variety of substances including contaminants, toxins, adulterants, herbicides and carcinogens. They use an enzyme as a label and visualization is achieved via conversion of the substrate to a colored product. There are different types of ELISA s i.e., competitive (Fig. 7), non-competitive (Fig. 8), sandwich (Fig. 9) and homogeneous enzyme immunoassay (48). 

Figure 14. Principle of homogeneous enzyme immunoassay (Reproduced with permission from Ref. 17. Copyright 1973 American Association for Clinical Chemistry, Inc.)...

Homogeneous Enzyme Immunoassay with Enzyme Prosthetic Group... 

Fig. 1. Schematic representation of the principle of homogeneous enzyme immunoassay developed by Rubenstein (emit). [Cited and modified from Fig. IV-4, Miyai, K., in Ishikawa et al., eds. (15).]...

G3. Gibbons, I., Skold, C., Rowley, G. L., and Ullman, E. F., Homogeneous enzyme immunoassay for proteins employing (3-galactosidase. Anal. Biochem. 102,167-710 (1980). 

N5. Ngo, T. T., and Lenhoff, H. M., Recent advances in homogeneous and separation-free enzyme immunoassays. Appl. Biochem. Biotechnol. 6, 53-64 (1981). 

A variety of immunoassay techniques employ changes in the fluorescent properties of molecules to measure drug concentrations. Labelling of drugs with such molecules avoids the hazards of working with radioisotopes. Fluoroimmunoassays (FIA) also offer enhanced sensitivity in comparison to enzyme immunoassays they may be homogeneous or heterogeneous. 

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