Bioluminescent assays of picomole levels of various metabolites using immobilized enzymes

Specific immobilization of in vivo biotinylated bacterial luciferase and FMN:NAD(P)H oxidoreductase

Bacterial bioluminescence, catalyzed by FMN:NAD(P)H oxidoreductase and luciferase, has been used as an analytical tool for quantitating the substrates of NAD(P)H-dependent enzymes. The development of inexpensive and sensitive biosensors based on bacterial bioluminescence would benefit from a method to immobilize the oxidoreductase and luciferase with high specific activity. Toward this end, oxidoreductase and luciferase were fused with a segment of biotin carboxy carrier protein and produced in Escherichia coli. The in vivo biotinylated luciferase and oxidoreductase were immobilized on avidin-conjugated agarose beads with little loss of activity. Coimmobilized enzymes had eight times higher bioluminescence activity than the free enzymes at low enzyme concentration and high NADH concentration. In addition, the immobilized enzymes were more stable than the free enzymes. This immobilization method is also useful to control enzyme orientation, which could increase the efficiency of sequentially operating enzymes like the oxidoreductase-luciferase system.

Use of genetically prepared enzyme conjugates in enzyme immunoassay

Enzyme immunoassay, using enzymes crosslinked to either antibodies or antigens, has proved a valuable immunological tool for many years. Recently, gene fusion techniques have been used to prepare these enzyme conjugates. This method may be especially advantageous in cases where (1) the antigen is difficult and costly to obtain in large quantities or (2) when the activity of the marker enzyme or the affinity of the antibody or antigen is severely reduced or even destroyed by use of conventional linking methods such as chemical crosslinking. This article uses specific examples to illustrate the potential of gene fusion as a conjugation method.

Characterization of a recombinant bifunctional enzyme, galactose dehydrogenase/bacterial luciferase, displaying an improved bioluminescence in a three-enzyme system

The two structural genes encoding galactose dehydrogenase (Pseudomonas fluorescens) and the beta subunit of luciferase (Vibrio harveyi) were fused in-frame in order to prepare and subsequently characterize an artificial bifunctional enzyme complex. This hybrid enzyme exhibited both galactose dehydrogenase activity and bioluminescence when expressed in Escherichia coli together with the alpha subunit of luciferase. The purified conjugate was used to study possible proximity effects in a sequential three-enzyme reaction with the bifunctional enzyme catalyzing the first and the last reaction. The intermediate enzyme, diaphorase, was added separately. The engineered enzyme system, comprising the galactose dehydrogenase/luciferase conjugate, could display a twofold higher bioluminescence in the overall enzyme reaction compared to a corresponding reference system with separate native enzymes. The increased bioluminescence obtained for the engineered enzyme system is proposed to be due to an improved organization of the enzyme in solution.

Preparation of a genetically fused protein A/luciferase conjugate for use in bioluminescent immunoassays

The genes encoding staphylococcal protein A and bacterial luciferase (Vibrio harveyi) were fused in-frame in order to obtain a general marker enzyme for bioluminescent immunoassays. Two constructs were made where protein A was ligated to the first and the 12th amino acid residue, respectively, of the N terminus of the beta subunit of luciferase. Only the first fusion protein encoding the entire beta subunit was able to form an enzymatically active luciferase complex when expressed together with the alpha subunit. The fusion of protein A to luciferase did not notably alter the emitted wavelength spectrum or its stability to urea treatment. The fusion protein was found to retain at least 50% of the specific bioluminescent activity compared to native luciferase. In preliminary tests, this hybrid protein was shown to be useful in bioluminescent immunoassays.

Chemiluminescence detection for high-performance liquid chromatography of biomedical samples

During recent years, much progress has been made in the development of high-performance liquid chromatographic (HPLC) detection systems based on chemiluminescence (CL). CL is now one of the most sensitive detection methods in HPLC. For many compounds detection limits in the femtogram to picogram range have been obtained. Several on-line post-column reactions have been used for chemical excitation of the analytes. Some theoretical aspects of CL detection are presented and special attention is devoted to the coupling of CL to flow systems. The influence of the kinetics of the reaction on the sensitivity of the detection system is stressed. The mechanisms and detection systems of the peroxyoxalate, luminol and lucigenin CL reaction are described. A few examples of the use of bioluminescence for HPLC detection are given, and some less common CL reactions used in flow systems are also mentioned. Many biomedical and related applications are shown. Possibilities and limitations of the various reactions and detection systems are evaluated.

A spectrophotometric assay for 6-phosphogluconolactonase involving the use of immobilized enzymes to prepare the labile 6-phosphoglucono-delta-lactone substrate

We report the development of a new spectrophotometric assay for 6-phosphogluconolactonase. The labile substrate 6-phosphoglucono-delta-lactone is prepared from glucose 6-phosphate by enzymes co-immobilized on Sepharose beads. The assay has the advantages of high sensitivity for routine determination of enzyme activity and allows determination of both Km and Vmax. from a single assay. A method for estimating the contribution of spontaneous hydrolysis to total hydrolysis is described. This assay overcomes the problems encountered with all previous assays.

Immobilized bacterial luciferase and its applications

This review discusses the properties of the bioluminescent bacterial system as well as the methods for immobilization of bacterial luciferases and for their co-immobilization with other enzymes. The analytical systems using immobilized bacterial luciferases and their applications in analytical biochemistry and biotechnology have been described.

Measurements of serum glucose using the luciferin/luciferase system and a liquid scintillation spectrometer

A single-step assay for serum glucose measurements is described. The assay is based on the phosphorylation of D-glucose by glucokinase and the measurement of ATP consumption by firefly luciferase. The luminescence is recorded in an ordinary liquid scintillation spectrometer. The use of stable reagents and a stable final signal (light emission) makes it possible to analyze a large number of samples in each assay run. The assay is of particular value when repeated serum glucose determinations are performed on samples from small laboratory animals.

Bioluminescent immunosorbent for rapid immunoassays

We describe a bioluminescent immunoassay procedure which does not require a separation step to remove excess free label. A luminescent immunosorbent constituted of bacterial luciferase, FMN oxidoreductase, and an antibody coimmobilized on Sepharose is used to determine specifically the label enzyme (glucose-6-phosphate dehydrogenase, coupled to an antigen) bound by a specific antibody. The immunosorbent confines the bioluminescent reaction in a small volume, and the bound label produces NADH, which is directly used by the nearby luciferase FMN oxidoreductase enzyme system. On the contrary NADH produced by dehydrogenases in solution is directly oxidized without emitting light. Dehydrogenases contained in the biological sample do not interfere with the assay, which can be performed directly on 25 microliter of serum. In this paper we describe the general procedure and we analyze the different parameters that must be optimized.

Determination of chenodiol bioequivalence using an immobilized multi-enzyme bioluminescence technique

Measurement of the bioequivalence of formulations of chenodiol, a bile acid which is used for gallstone dissolution, is difficult because its high first-pass clearance results in low plasma levels after ingestion of usual dosages. To solve this problem, a new method was developed to determine the bioequivalence of several chenodiol formulations. The method included the following steps: isolation of all bile acids from serum by absorption to a hydrophobic resin, elution of bile acids from the resin by methanol, separation of the unconjugated bile acid fraction by an ion-exchange procedure, and bioluminescence measurement of the unconjugated 7 alpha-hydroxy bile acids using Sepharose beads containing co-immobilized 7 alpha-hydroxysteroid dehydrogenase, diaphorase, and luciferase. The isolation method gave complete recovery, and the bioluminescence procedure was simple, rapid, and sensitive. The peak level of systemic chenodiol occurred 1 to 2 h following oral ingestion and ranged from 4 to 8 microM. This method appears superior to previously reported methods for determining the bioequivalence of chenodiol preparations. In principle, the method is suitable for measurement of the bioequivalence of other bile acids provided the appropriate hydroxysteroid dehydrogenase is available.

Bioluminescent assays using coimmobilized enzymes

In summary the use of immobilized luciferases along with other enzymes offers a method for measuring a wide variety of metabolites or enzymes. The assays are rapid, sensitive, and specific and can be automated. It is anticipated that many more assays for different compounds will be developed in the future.

A sensitive kinetic assay for glycerol using bacterial bioluminescence

A kinetic assay method based on bacterial bioluminescence and the glycerol dehydrogenase (GDH) enzyme reaction has been developed for the determination of glycerol. The assay system involves the use of three coupled enzyme reactions in which the participating reactants are optimized to allow internal calibration by known amounts of glycerol. This bioluminescent assay method is also suitable for measuring GDH enzyme activity. The lower detection limit for glycerol is 500 pmol and for GDH, 0.001 mU, the assay being linear up to 300 nmol of glycerol and 3 mU of GDH. The percentage recovery of glycerol from serum was 95-100%. This assay method is rapid, sensitive, and reproducible.

The analysis of picomole amounts of L(+)- and D(-)-lactic acid in samples of dental plaque using bacterial luciferase

L(+)-Lactic acid (5 pmol) and D(-)-lactic acid (20 pmol) were assayed by coupling the generation of NADH with the use of bacterial luciferase. The binding of NADH to L(+)-lactic dehydrogenase made it necessary to denature the protein so that the assay with bacterial luciferase was effective. The coupled luciferase assay of L(+)-lactic acid was 400 times more sensitive than the fluorometric assay. The luciferase coupled assay was used to analyze the L(+)- and D(-)-lactic acid contents of small samples of dental plaque.

Bioluminescent assay of femtomole levels of estrone and estradiol

A rapid and very sensitive enzymatic assay of estrogens was developed using the transhydrogenase reaction of the human estradiol-17 beta dehydrogenase and bioluminescence for the quantification of NADH accumulated during the first reaction. The assay requires two steps: first, the addition of transhydrogenase buffer, and a few minutes later the addition of the bioluminescence reagent. The method can determine 0.1 to 50 pg of estrogens in the assay, in 1 h, with a coefficient of variation of 5%.