Evaluation of beta-D-galactosidase from Escherichia coli and horseradish peroxidase as labels by sandwich enzyme immunoassay technique.

beta-D-galactosidase from Escherichia coli and horseradish peroxidase were evaluated as labels of Fab' in dose-response curves for human alpha-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'-beta-D-galactosidase conjugates, and the affinity-purified Fab'-peroxidase conjugates gave more sensitive dose-response curves for these antigens than the corresponding beta-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 beta-D-galactosidase assay. Other advantages and disadvantages of the two enzymes are discussed.