This immunoassay kit allows for the specific measurement of total rat Activin A concentrations in cell culture supernates, serum, and plasma.

 

Activins and inhibins, members of the TGF-β superfamily, are disulfide-linked dimeric proteins that were originally purified from gonadal fluids as proteins that stimulated or inhibited, respectively, pituitary follicle stimulating hormone (FSH) release. These proteins have since been shown to have a wide range of biological activities including: mesoderm induction, neural cell differentiation, bone remodeling, hematopoiesis and reproductive physiology. Activins/inhibins are produced as precursor proteins with an amino-terminal propeptide that is cleaved to release the carboxy-terminal bioactive ligands. Activins are homodimers or heterodimers of the various β subunit isoforms, while inhibins are heterodimers of a unique α subunit and one of the various β subunits. Five β subunits (mammalian βA, βB, βC, βE and Xenopus βD) have been cloned to date. The activin/inhibin nomenclature reflects the subunit composition of the proteins: activin A (βA - βA), activin B (βB - βB), activin AB (βA - βB), inhibin A (α - βA) and inhibin B (α - βB). At present, little is known about the contribution of the other β subunits to activin or inhibin formation and biology. At the amino acid sequence level, the mature human βA subunit is 100% identical to mouse βA, while the human and mouse α subunits share approximately 80% identity. Similarly to other TGF-β family members, activins exert their biological activities through binding to the heterodimeric complex composed of two membrane spanning serine-threonine kinases designated type I and type II. Two forms of activin receptor type I (Act RI-A and Act RI-B) and two forms of activin receptor type II (Act RII-A and Act RII-B) have been identified. Activin binds directly to Act RII, the complex then associates with Act RI and initiates signaling. Besides activins, Act RII has been shown to bind certain other TGF-β superfamily members. Inhibin A has been shown to bind with low-affinity to Act RII. The existence of a distinct inhibin-specific receptor and/or signal transduction pathway has been hypothesized

 

This assay employs the quantitative sandwich enzyme immunoassay technique. A monoclonal antibody specific for Activin A has been pre-coated onto a microplate. Standards and samples are pipetted into the wells and any Activin A present is bound by the immobilized antibody. An enzyme-linked monoclonal antibody specific for Activin A is added to the wells. Following a wash to remove any unbound antibody-enzyme reagent, a substrate solution is added to the wells and color develops in proportion to the amount of Activin A bound in the initial step. The color development is stopped and the intensity of the color is measured.