Abstract: A highly sensitive, immunoassay method for determining the amount of an analyte in a sample containing a known analyte in an unknown concentration is provided. Sample; a polypeptide-labeled analog of the analyte, an antibody specific for said analyte, a polypeptide partner capable of non-covalently binding with the polypeptide-labeled analyte to form a complex having catalytic activity, and a substrate capable of being converted to a reporter molecule by the catalytic activity of said complex are brought together in a medium. The polypeptide-labeled analyte analog is capable of competitively binding to the antibody and the polypeptide partner, the antibody inhibiting the formation of a catalytically active complex in the absence of analyte, and the concentration of the antibody, polypeptide partner and polypeptide-labeled analyte are such as to cause varying amounts of analyte to be directly related to the conversion of the substrate to the reporter molecule.

Abstract: A method for preparing a substrate capable of undergoing catalytic-induced hydrolysis of the phosphate ester at the 3' position, to yield a species capable of being monitored spectrophotometrically or fluorometrically, comprises(a) forming a mononucleotide 20', 3' cyclic phosphate of the formula: ##STR1## wherein B is a nucleotide base, and wherein the CH.sub.

Abstract: Novel substrates for monitoring of catalytic activity resulting in hydrolytic release of products which can be readily detected by spectrophotometric or fluorometric means are provided. The substrates have the general formula: ##STR1## wherein B is a nucleotide base capable of assisting in hydrolysis of the phosphate ester at the 3'-position; R is a moiety selected from the group consisting of umbelliferonyl, 4-methylumbelliferonyl, 3-flavonyl, o-nitrophenyl, m-nitrophenyl, p-nitrophenyl, dinitrophenyl, cyanophenyl, acylphenyl, carboxyphenyl, phenylsulfonate, phenylsulfonyl and phenylsulfoxide; R' is a moiety selected from the group consisting of hydrogen, alkyl, alkenyl cycloalkyl, aryl, araalkyl, acyl, oxaalkyl, thioalkyl, oxacycloalkyl, and thiocycloalkyl and R" is hydrogen or a cation selected from the group consisting of calcium, barium, lithium, sodium, ammonium, substituted ammonium and pyridinium.

Abstract: A highly sensitive, immunoassay method for determining the amount of an analyte in a sample containing a known analyte in an unknown concentration is provided. Sample; a polypeptide-labeled analog of the analyte, an antibody specific for said analyte, a polypeptide partner capable of non-covalently binding with the polypeptide-labeled analyte to form a complex having catalytic activity, and a substrate capable of being converted to a reporter molecule by the catalytic activity of said complex are brought together in a medium. The polypeptide-labeled analyte analog is capable of competitively binding to the antibody and the polypeptide partner, the antibody inhibiting the formation of a catalytically active complex in the absence of analyte, and the concentrations of the antibody, polypeptide partner and polypeptide-labeled analyte are such as to cause varying amounts of analyte to be directly related to the conversion of the substrate to the reporter molecule.

Abstract: Folic acid derivatives, such as radiolabeled pteroyltyrosine, are conveniently synthesized from either pteroic acid or by the direct condensation of 6-formylpterin with p-aminobenzoyltyrosine methyl ester. The radioiodinated derivatives are particularly useful in competitive protein binding and radioimmuno-assays of folate compounds.