The MaxDiscovery™ Aspartate Transaminase (AST) Cytotoxicity Kit is a plate-based colorimetric enzymatic assay for the determination of the aspartate transaminase enzyme in cultured cell lines. Aspartate transaminase (AST) also known as aspartate aminotransferase or (sGOT) is a metabolic enzyme expressed in a host of mammalian cell types. Upon cell damage or lysis the enzyme is released into the cell culture supernatant and is thus a useful tool for the investigation of cytotoxicity effects of experimental drug formulations and cell transfection. The MaxDiscovery™ Alanine Transaminase (AST) Cytotoxicity Assay Kit uses a coupled enzymatic reaction scheme: aspartate and a-ketoglutarate are first converted to glutamate and oxaloacetate which is converted by malate dehydrogenase to make malate and NAD+. The conversion of the NADH chromophore to NAD+ product, measured at 340 nm, is proportional to the level of AST enzyme in the sample. The absorbance of each well at 340 nm is measured using a plate reader. The concentration of AST in each sample is then directly determined from the change in absorbance at 340 nm over a 30 minute assay length. Although AST is present in a host of human tissues, its release varies among cell types. Therefore, the most useful analysis of cytotoxicity in a cultured cell line involves measuring cytotoxicity as a percentage of damaged or lysed cells.