Abstract
β-d-galactosidase from Escherichia coli and horseradish peroxidase were evaluated as labels of Fab' in dose-response curves for human α-fetoprotein and human chorionic gonadotropin by sandwich enzyme immunoassay technique using fluorogenic substrates for enzyme assay. The non-specific binding of Fab'–peroxidase conjugates to IgG-coated polystyrene balls was less than that of Fab'-β-d-galactosidase conjugates, and the affinity-purified Fab'–peroxidase conjugates gave more sensitive dose-response curves for these antigens than the corresponding β-d-galactosidase conjugates. However, a large quantity of Fab'–peroxidase conjugates was required and a longer incubation was necessary for the peroxidase assay, since the peroxidase assay was much less sensitive than the β-d-galactosidase assay. Other advantages and disadvantages of the two enzymes are discussed.