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 s imultaneous determination of guanase and aspartate aminotransferase (A ST) activities in a single serum sample is described. The method is ba sed on direct detection of enzymatically formed products xanthine and glutamate, respectively. The procedure is sensitive, precise (C.V. bel ow 2% for guanase and 3% for AST), suitable for routine purposes and r equires only 100 mu l of sample. Kinetic measurements have shown the g uanase activity to have an apparent Michaelis constant of 24.5 mu M an d the AST activity of 11.1 and 0.18 mM for aspartate and oxoglutarate, respectively, at 37 degrees C in Tris-HCl buffer (pH 7.5).