Properties of bacterial luciferase/NADH : FMN oxidoreductase and firefly luciferase immobilized onto sepharose

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Abstract
NADH : FMN oxidoreductase and bacterial luciferase have been efficiently coimmobilized onto Sepharose 4B. This luminescent immobilized enzyme system can be used to assay NADH. The assay is rapid and sensitive with a lower limit of detection of 0.2 pmol/assay tube. The intra-assay precision was 3.5% at 2 × 10-5 M and 5.8% at 2 × 10-6 M NADH. Light intensity was proportional to NADH concentration from 0.2 to 1000 pmol. Added serum and certain dehydrogenases were found to be inhibitory; however, inhibition could be eliminated by a combination of heat treatment and dilution. Firefly luciferase has also been immobilized onto both Sepharose 4B and CL 6B. The detection limit for ATP using this immobilized enzyme was 0.2 pmol and the assay was linear from 0.2 to 2000 pmol. The intra-assay precision was 4.8% at 2 × 10-4 M and 3.2% at 1 × 10-5 M ATP. The immobilized enzymes remained fully active when rapidly frozen in the presence of glycerol and DTT. Such preparations could be stored for at least two months with no loss of activity. A variety of different compounds were used to block any remaining reactive groups on the Sepharose following immobilization of the enzymes. Glycine, 2-aminoethanol, and ethylenediamine were examined. The preparations where ethylenediamine was used as a blocking agent exhibited better activity and stability than the others.