Abstract: Enzyme-donor fragments and other unstructured peptides are stabilized against proteolytic degradation by including a mixture of soluble, random-sequence peptides in the assay medium or in the medium in which the enzyme-donor fragment or other peptide is stored.

Abstract: Diagnostic assays are provided comprising complementary enzyme fragments of .beta.-galactosidase, where one of the fragments is bound to a support and the other fragment is conjugated to an immunologically cross-reactive epitope of the analyte or complementary to an analyte receptor. Binding to the receptor allows for discrimination between complexed enzyme fragment conjugate and uncomplexed enzyme fragment conjugate. The assay medium is then allowed to wick onto a support to which the complementary fragment is substantially uniformly bound in the detection region. The support is then developed, where color formation from the substrate in the detection region is used as a measure of the presence of analyte in the sample.

Abstract: This invention relates to improved methods and novel compositions for enzyme complementation assays for qualitative and quantitative determination of a suspected analyte in a sample. The use of enzyme-acceptor and enzyme-donor polypeptides prepared by recombinant DNA techniques, DNA synthesis or chemical polypeptide synthesis techniques which are capable of interacting to form an active enzyme complex having catalytic activity characteristic of .beta.-galactosidase is described. Both homogeneous and heterogeneous assays utilizing these polypeptides are described.

Abstract: A .beta.-galactosidase complementation assay for determining the presence of an analyte which is a member of a specific binding pair (sbp) in a sample is provided, which assay permits visual discrimination between those samples wherein the analyte is present above a predetermined, threshold concentration. The method comprises combining the sample with a hydrophobic enzyme donor- (ED-) analyte conjugate and the complementary member of the sbp to form an sbp complex-containing assay medium. A small volume of the assay medium is spotted onto an enzyme acceptor (EA) affixed to a bibulous, solid support, followed by development with enzyme substrate solution. A substantially larger area is detectable when analyte in the sample is below as compared to above a threshold concentration. The assay is particularly useful in field testing applications such as determining the presence of antibiotics in milk, toxins in water, or drugs in serum or urine. Kits facilitating the method are also provided.

Abstract: A method is provided for combining normally interacting reagents in a liquid single reagent and preventing complex formation using a surfactant and then reversing the inhibition by adding a cyclodextrin. The method finds particular use in diagnostic immunoassays. Reagents facilitating the invention are also provided.

Abstract: A method of stabilizing .beta.-galactosidase peptide fragments against storage degradation for use in a complementation assay which comprises storing the peptide fragment in a storage medium containing an ionic surfactant or a surfactant derived from a sugar residue and adding a cyclodextrin to the storage medium after storing the peptide fragments but before using them in a complementation assay.

Abstract: Serum samples for vitamin B.sub.12 analysis can be pretreated using a combination of peroxy acid and dithiothreitol. The pretreatment makes vitamin B.sub.12 bound to serum binding proteins available for analysis by any of a variety of currently available assay techniques. The pretreatment finds particular use in an assay using solid phase intrinsic factor as a specific binding protein.

Abstract: This invention relates to improved methods and novel compositions for enzyme complementation assays for qualitative and quantitative determination of a suspected analyte in a sample. The use of enzyme-acceptor and enzyme-donor polypeptides prepared by recombinant DNA techniques or chemical polypeptide synthesis techniques which are capable of interacting to form an active enzyme complex having catalytic activity characteristic of .beta.-galactosidase is described. Both homogeneous and heterogeneous assays utilizing these polypeptides are described.