Enzymatic activity of ASS1 was examined by di-phosphate release from the argininosuccinate synthesis reaction. whole cell extracts prepared from SW-1116 cells expressing LOC113230, shLOC113230, or vector were subjected for in vitro ASS1 enzymatic assays, and purified enzymatic dead mutant ASS1 K165Q and ASS1 K176Q proteins were used as controls. 