Immobilized enzymes are widely used for clinical and industrial purposes for the assay of different analytes and enzymes. At the same time, the continuing quest for sensitive non-radioactive methodologies, has contributed to a rapidly expanding repertoire of bioluminescent assays for metabolite, hormones, drugs, and even explosives. The immobilization of an enzyme generally results in increased stability and the additional property of reusability, while retaining specificity for substrates and effectors. The immobilized enzyme can be used as an analytical tool in place of its soluble counterpart with the added advantages of easier handling and decreased cost. Bacterial luciferases catalyze the luminescence reaction utilizing FMNH_2, a long chain aliphatic aldehyde and O_2, to produce blue-green light at 490 nm. This light-emitting system is particularly attractive for use in bioassays as it is readily available, the substrates are very inexpensive and it can be readily coupled to formation of NAD(P)H generated on oxidation of a wide variety of different biological compounds. In the present work we have immobilized different bacterial luciferases on alkyl-substituted Sepharose 4B and examined them for activity and stability. In addition, exposure of hydrophobic clusters in the protein molecule was confirmed by fluorescence studies using 8-anilino-1-napthalene-sulfonate as a hydrophobic-reporter probe. Characterization of the properties of the immobilized luciferases demonstrated that not only did they retain a substantial part of their activity without a change in kinetic properties but the thermal stability of both Vibrio harveyi and Xenorhabdus luminescens immobilized luciferases were enhanced providing a stable, reusable and effective source of luciferase for use as a light-emitting sensor in bioassays.
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