Stable and versatile active acridinium esters II.

The synthesis of acridinium esters with a linking group directly attached to the acridine nucleus is described. This strategy will allow the widest possible choice of variously substituted phenyl esters without restricting them to those structures bearing linking groups on the phenol.

Stable and versatile active acridinium esters I.

The synthesis of acridinium esters with a linking group directly attached to the acridine nucleus is described. This strategy will allow the widest possible choice of variously substituted phenyl esters without restricting them to those structures bearing linking groups on the phenol.

Membrane-permeable luciferin esters for assay of firefly luciferase in live intact cells.

Five esters of luciferin were synthesized and compared with native luciferin as substrates for firefly luciferase expressed in live intact mammalian cells. The esters themselves were not substrates for purified luciferase, but four were substrates for a purified esterase and all appeared to be hydrolysed to luciferin within mammalian cells. At a substrate concentration of 0.01 mM, the peak luminescence from the cos cells expressing luciferase was up to 6-fold greater with the esters than with unmodified luciferin. At 0.1 mM, the difference between luciferin and the esters was decreased. The kinetics of the luminescent signal with the different luciferin esters varied significantly, indicating possible differences in the rates of uptake, breakdown and enzyme inhibition. The esters did not support luminescence from Escherichia coli cells expressing firefly luciferase, suggesting a lack of appropriate esterase activity in this particular strain. The esters could be useful for the assay of luciferase expression in intact mammalian cells when luciferin levels are limiting, for example in tissues, and in plants. Alternative luciferin derivatives may allow further improvements in sensitivity.

Formation of the Ca2+-activated photoprotein obelin from apo-obelin and mRNA inside human neutrophils.

1. A method has been developed to incorporate the apoprotein of the Ca2+-activated photoprotein obelin, and mRNA purified from the hydroid Obelia, into the cytoplasm of intact human neutrophils. This was based on internal release from pH-sensitive immunoliposomes taken up initially by phagocytosis. 2. Addition of the prosthetic group of obelin, coelenterazine, to these cells containing apo-obelin or Obelia mRNA resulted in formation of active Ca2+-activated obelin. 3. The obelin formed within the neutrophils responded to the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (1 microM) and to the membrane attack complex of complement (C5B6789n). 4. The formation of the apo-obelin from mRNA within neutrophils was inhibited by over 80% in the absence of added amino acids, and by over 90% by the protein-synthesis inhibitor puromycin (100 micrograms/ml). 5. The translation of Obelia mRNA inside cells provides a method for circumventing consumption of Ca2+-activated photoproteins during cell activation or injury, and for monitoring protein synthesis in living cells.

Chemiluminescence immunoassay of plasma progesterone, with progesterone-acridinium ester used as the labeled antigen.

This simple solid-phase chemiluminescence immunoassay for measurement of progesterone in extracts of venous plasma has sensitivity and precision similar to that of conventional radioimmunoassay with use of a tritiated antigen. The labeled antigen, 11 alpha-progesteryl-2-succinoyltyramine-4-(10-methyl)-acridini um-9-carboxylate, and a monoclonal antibody to progesterone-11 alpha-succinyl-bovine serum albumin are incubated with a 100-microL aliquot of plasma extract (equivalent to 20 microL of plasma) and 50 microL of a suspension of an IgG fraction of a donkey antiserum to mouse immunoglobulins, covalently attached to cellulose particles. After the antibody-binding reaction (60 min at 4 degrees C), 1 mL of phosphate buffer is added to each tube, the tubes are centrifuged (5 min, 1500 X g), and the supernatant fluid is aspirated. The washing step is repeated and diluted hydrochloric acid (50 mmol/L, 50 microL) is added to the pellet. Luminescence is initiated by oxidation with dilute sodium hydroxide/hydrogen peroxide. The signal is integrated over 10 s. The light yield is inversely proportional to the progesterone concentration in the standard or sample.

Acridinium esters as high-specific-activity labels in immunoassay.

A chemiluminescent acridinium ester has been synthesized that reacts spontaneously with proteins to yield stable, immunoreactive derivatives of high specific activity. The compound has been used to prepare chemiluminescent monoclonal antibodies to human alpha 1-fetoprotein having average incorporation ratios as great as 2.8 mol of label per mole of antibody, which corresponds to a detection limit of approximately 8 X 10(-19) mol. These antibodies have been used in the preliminary development of a two-site immunochemiluminometric assay for human alpha 1-fetoprotein, which requires only a 30-min incubation and a quantification time of 5 s per sample.

Chemiluminescence energy transfer: a new technique applicable to the study of ligand--ligand interactions in living systems.

Chemiluminescent molecules can be readily detected in the range 10(-15) to 10(-18) mol, and potentially at least down to 10(-20) mol reacting/s. The chemiluminescent compound aminobutylethylisoluminol (ABEI) and its isothiocyanate derivative have been synthesized. The ABEI was coupled to rabbit immunoglobulin and cyclic AMP. These labeled antigens were stable for at least 9 months and were used to establish chemiluminescent immunoassays. When these chemiluminescent-labeled antigens bound to their respective fluorescein-labeled antibodies, a wavelength shift towards the green was detected in the chemiluminescence. This was due to chemiluminescence energy transfer and used to establish an homogenous immunoassay which could measure these antigens in biological samples at least as sensitively as conventional radioimmunoassays.