A sensitive enzyme-linked immunosorbent assay for dihydrofolate reductase.

A competitive enzyme-linked immunosorbent assay (ELISA) has been developed for the enzyme, dihydrofolate reductase. The sensitivity of the assay system approximates 3 ng of immunoreactive enzyme protein which is comparable to the sensitivity achieved in the radioimmunoassay (RIA) for this enzyme. The mean coefficient of variation for within--and between--assay precision was less than 13%. The assay appears to be specific and valid as the concentration of the enzyme is the same whether measured by ELISA or [3H]-methotrexate binding. Since this method, like the RIA, measures the mass concentration of enzyme protein, in conjunction with a [3H]-methotrexate binding assay it will be useful for quantitating functional as well as non-functional immunoreactive forms of the enzyme.