Electrochemiluminescence (ECL) detection reagents and related methods for measuring enzyme activity
Disclosed are methods of measuring enzyme activity in a sample. The methods use disulfide-containing detection reagents with an electrochemiluminescent functional group.
1. A detection reagent, comprising:
a molecule having a cleavable disulfide bond with an electrochemiluminescence (ECL)-active ruthenium chelate on a first side of the disulfide bond and an immobilizing moiety on a second side of the disulfide bond, wherein the disulfide bond of the detection reagent is capable of being cleaved by a free sulfhydryl group, and
wherein the free sulfhydryl group is exposed by one or more components in a reaction mixture,
the molecule which is measurable within the reaction mixture by the absence, presence or amplitude of an ECL signal, wherein the cleaving by the free sulfhydryl group is in proportion to the amount of enzyme generated in the sample.
2. A method of preparing the detection reagent of claim 1 , comprising:
attaching to a molecule having a disulfide bond, an electrochemiluminescence (ECL)-active ruthenium chelate on a first side of the disulfide bond and an immobilizing moiety on a second side of the disulfide bond.
3. The method of claim 2 , wherein the disulfide bond of the detection reagent is capable of being cleaved by a free sulfhydryl group.
4. A method of preparing the detection reagent of claim 1 , comprising:
attaching an electrochemiluminescent functional group to a first molecule having a sulfide group capable of forming a disulfide bond;
attaching an immobilizing moiety to a second molecule having a sulfide group capable of forming a disulfide bond; and
forming a cleavable disulfide bond between the first molecule and the second molecule.
5. The method of claim 4 , wherein the disulfide bond of the detection reagent is capable of being cleaved by a free sulfhydryl group.
6. A method of preparing the detection reagent of claim 1 , comprising:
forming a cleavable disulfide bond between a first molecule and a second molecule;
attaching an electrochemiluminescent functional group to the first molecule; and
attaching an immobilizing moiety to the second molecule.
7. The method of claim 6 , wherein the disulfide bond of the detection reagent is capable of being cleaved by a free sulfhydryl group.
8. A method for measuring NADPH generated in a sample, comprising:
combining the detection reagent of claim 1 having a disulfide bond, the sample and an NADPH-catalyzed disulfide reductase to form a reaction mixture, wherein the disulfide bond of the detection reagent is cleaved by the reductase in the presence of NADPH,
wherein the cleaving yields a first cleavage product having the ECL-active ruthenium chelate and a second cleavage product having the immobilizing moiety, and
wherein the cleaving by the reductase is in proportion to the amount of NADPH generated in the sample; and
measuring the absence, presence or amplitude of an ECL signal, wherein the absence or reduced magnitude of an ECL signal indicates the presence of NADPH in the sample, and wherein a maximal ECL signal indicates the absence of NADPH in the sample.
9. The method of claim 8 , wherein the NADPH is generated by glucose-6-phosphate dehydrogenase.
10. The method of claim 8 , wherein the disulfide-cleaving reductase is chosen from glutathione reductase and trypanothione reductase.
11. The methods of claim 8 , wherein the immobilizing moiety is biotin.
12. A method for measuring NADPH-generating enzyme activity in a sample, comprising:
(a) combining the sample, NADP+, and a substrate specific to the enzyme to be measured within the sample, to form a reaction mixture under conditions such that NADPH is generated from reduced NADP+;
(b) combining the reaction mixture of step (a) with glutathione reductase and glutathione disulfide under conditions that will reduce glutathione disulfide to GSH;
(c) combining the reaction mixture of step (b) with the detection reagent of claim 1 , wherein the disulfide bond of the detection reagent is cleaved nonenzymatically by the reduced glutathione,
wherein the cleaving by the reduced glutathione is in proportion to the amount of NADPH generated in the sample; and
(d) measuring the absence, presence or amplitude of an ECL signal, wherein the absence or reduced magnitude of an ECL signal indicates the presence of NADPH-generating enzyme in the sample, and wherein a maximal ECL signal indicates the absence of NADPH-generating enzyme in the sample.
13. The method of claim 12 , wherein step (a) is carried out over a specified time and at a specified temperature.
14. The method of claim 12 , wherein the NADPH-generating enzyme is glucose-6-phosphate dehydrogenase.
15. The methods of claim 12 , wherein the immobilizing moiety is biotin.
16. A method for measuring esterase activity in a sample, comprising:
combining the sample, a thioester analog of a substrate for an esterase, and the detection reagent of claim 1 , to form a reaction mixture, under conditions such that the thioester analog of the substrate is deacylated by esterase in the reaction mixture to yield an activated substrate analog having an exposed deacylated free sulfhydryl group which cleaves the disulfide bond of the detection reagent leading to a change in a detectable ECL signal in proportion to the esterase activity in the reaction mixture; and
measuring the absence, presence or amplitude of an ECL signal, wherein the absence or reduced magnitude of an ECL signal indicates the presence of esterase in the sample, and wherein a maximal ECL signal indicates the absence of esterase in the sample.
17. The method of claim 16 , wherein the esterase is Lp-PLA 2 (platelet activating factor acetylhydrolase).
18. The method of claim 16 , wherein the thioester analog of a substrate is chosen from thio-platelet activating factor (PAF), lyso-thio-PAF, acetylthiocholine, propionylthiocholine and butyrylthiocholine.
19. The method of claim 16 , wherein the immobilizing moiety is biotin.
20. The method of claim 16 , the combining step further comprising combining a detergent.
21. The method of claim 20 , wherein the detergent is chosen from CHAPS (cholamidopropyl)dimethylammonio]-1-propanesulfonate) and Triton™ X-100 (4-(1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol, t-Octylphenoxypolyethoxyethanol, Polyethylene glycol tert-octylphenyl ether).
22. The method of claim 16 , further comprising the step of adjusting the pH after the combining step and before the measuring step.
23. A kit for measuring esterase activity in a sample, comprising:
the detection reagent of claim 1 ;
a thioester analog of a substrate for an esterase; and
instructions for performing an esterase activity measuring assay including the steps of
combining the sample, a thioester analog of a substrate for an esterase, and the detection reagent, to form a reaction mixture, under conditions such that the thioester analog of the substrate is deacylated by esterase in the reaction mixture to yield an activated substrate analog having an exposed deacylated free sulfhydryl group which cleaves the disulfide bond of the detection reagent leading to a change in a detectable ECL signal in proportion to the esterase activity in the reaction mixture; and
measuring the absence, presence or amplitude of an ECL signal, wherein the absence or reduced magnitude of an ECL signal indicates the presence of esterase in the sample, and wherein a maximal ECL signal indicates the absence of esterase in the sample.
24. The kit of claim 23 , wherein the esterase activity measuring assay measures the activity of an esterase selected from the group consisting of a lipase and a cholinesterase.
25. The kit of claim 23 , wherein the esterase is a lipase.
26. The kit of claim 23 , wherein the lipase is Lp-PLA 2 (platelet activating factor acetylhydrolase).