| abstract |
A trifunctional conjugate is provided having three chemical moieties attached through a spacer moeity. At least two of the chemical moieties are relatively small molecules, usually less than about 7,000 Daltons in size. The spacer moiety is selected to impart certain steric properties to the conjugate. In one embodiment, the binding of a macromolecular specific binding partner to one of the chemical moieties sterically inhibits the binding of a different macromolecule to another chemical moiety. In another embodiment, the binding of a first chemical moiety to a macromolecule restricts the subsequent binding of a second chemical moiety to a proximate location on the same macromolecule. The three chemical moieties are preferably a nitrophenylazido residue, a phenyl boronic acid residue, and a solid support or a label such as biotin. The spacer is preferably cysteine, lysine, glutamic acid, pyroglutamic acid, S-acetylmercaptosuccinic anhydride or omega -carbobenzoxylysine. The conjugate is useful in immunoassays and for targeted labeling of proteins. In an assay, a sample is contacted with the conjugate, a limited quantity of analyte binding partner and an excess of small molecule binding partner. Presence of the analyte is determined by detecting the amount of analyte binding partner diverted away from analyte attached to the spacer of the conjugate. |