The MaxDiscovery™ In Cell ELISA Kit is an enzyme immunoassay for quantitative protein analysis directly in adherent cell cultures—there is no need to lyse cells or run protein gels. The technique can be thought of as an ELISA performed on fixed, permeablized cells rather than on immobilized antigen. Like most ELISA assays, protein is detected using a series of two antibodies, a primary antibody for the protein of interest (not provided with the kit) and an enzyme-conjugated secondary antibody. The protein:antibody complex is visualized by adding an enzyme substrate that, when catalyzed, changes the color of the assay solution within the well of the tissue culture plate so that it can be read in a spectrophotometer at 450 nm. The relative amount of protein in the cells will be directly proportional to the amount of signal that is obtained, making this a simple, convenient, and accurate technique for quantifying specific protein levels within cell lines. The MaxDiscovery™ In Cell ELISA Kit contains materials for washing, fixing, and permeablizing cells in culture. HRP-conjugated anti-mouse and anti-rabbit secondary antibodies are included in the kit so that user-supplied primary antibodies from either mouse or rabbit may be used for detection of the protein of interest. In addition, the kit includes mouse-derived antibody targeting glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDH is one of the key enzymes involved in glycolysis, and because of its high-level, and constitutive expression, it is widely used as a loading control for Northern/Western blots and for protein normalization. The quantity of GAPDH in a sample is directly proportional to the number of cells in the sample. GAPDH expression is often used as an internal control in gene expression studies. Typically, GAPDH expression is used to normalize expression signal from the gene-of-interest with respect to cell number. This has been particularly useful for RNAi studies or other drug treatment studies. The MaxDiscovery™ In Cell ELISA assay makes it easy to quickly measure levels of GAPDH (positive control) or your protein-of-interest directly in cultured cells for relative quantitative analysis.