Practice question

ELISA depends on enzymes conjugated to antibodies that convert substrates into detectable signals with high turnover. Horseradish peroxidase, alkaline phosphatase and beta-galactosidase are classical labels because they are stable, possess high catalytic rates and produce colored or luminescent products from TMB, pNPP or ONPG. RNA polymerase synthesizes RNA from DNA template and has no chromogenic substrate useful for immunoassay readout. It lacks conjugation chemistry suitability and would not amplify signal under ELISA conditions, so it finds no routine application in immunodetection systems despite central role in transcription.