A new reducing agent of flavins and its application to the assay of bacterial luciferase.

Copper(I) plus ethylenediaminetetraacetic acid, Cu(I)-EDTA, reduces flavins. Using Cu(I)-EDTA reduction of riboflavin 5'-phosphate, a new assay method for bacterial luciferase is established. In previous assay methods, flavin and aldehyde substrates for luciferase have been routinely added to luciferase at different times; the new assay permits aldehyde and Cu(I)-reduced flavin to be injected simultaneously into air-saturated buffer containing luciferase. In the new assay method using Cu(I), bovine serum albumin is not required, the initial emission intensity is more than twice and the overall yield is about twice of that in the so-called standard assay for luciferase.