Use of malate dehydrogenase immobilized on the dialyzer groove of the Autoanalyzer II for serum aspartate aminotransferase determination

Malate dehydrogenase (EC 1.1.1.37) was immobilized on the lower groove of the dialyzer plate used for serum aspartate aminotransferase determination in the AutoAnalyzer II system. Immobilization was effected by covalently attaching malate dehydrogenase to the inner surface of the groove which was previously activated by treatment with glutaraldehyde at room temperature. The immobilized malate dehydrogenase catalyzed the reaction between oxaloacetate and NADH to form NAD in the coupled reaction originally proposed by Karmen. Results of the present method correlated well with those obtained by the Technicon SMA II system in which malate dehydrogenase is in solution (n = 99; r = 0.99; t = 0.30). The activity of immobilized malate dehydrogenase on the dialyzer groove was sufficient to measure serum aspartate aminotransferase for at least one month with continuous use. The stability of immobilized malate dehydrogenase was also dependent on the number of samples determined. The dialyzer plate is a reusable solid matrix for malate dehydrogenase immobilization. The expense of the present method is only half the cost of the method in which malate dehydrogenase is in solution.