Simultaneous assay for aspartate aminotransferase and guanase in human serum by high-performance liquid chromatography

A simple high-performance liquid chromatography (HPLC) assay for the simultaneous determination of guanase and aspartate aminotransferase (AST) activities in a single serum sample is described. The method is based on direct detection of enzymatically formed products xanthine and glutamate, respectively. The procedure is sensitive, precise (C.V. below 2% for guanase and 3% for AST), suitable for routine purposes and requires only 100 μl of sample. Kinetic measurements have shown the guanase activity to have an apparent Michaelis constant of 24.5 μM and the AST activity of 11.1 and 0.18 mM for aspartate and oxoglutarate, respectively, at 37°C in Tris-HCl buffer (pH 7.5).