Determination of alanine aminotransferase and aspartate aminotransferase with immobilised enzymes and electrochemical detection

A method for the determination of alanine aminotransferase and aspartate aminotransferase is described based on the oxidation of the dehydrogenase enzyme cofactor NADH at a platinum electrode polarised at 700 mV. This oxidation generates a steady-state current which is proportional to the concentration of the cofactor. Hence the rate of consumption of NADH in such reactions can be measured amperometrically and related to the activity of the dehydrogenase enzyme or to the activity of some other enzyme coupled to the dehydrogenase enzyme reaction. The principle of the method is first illustrated by the determination of lactate dehydrogenase in aqueous and serum samples. Then, after co-immobilising lactate dehydrogenase and malate dehydrogenase on a collagen membrane placed on the surface of a platinum electrode, alanine aminotransferase and aspartate aminotransferase are determined. No significant decrease in the activity of the immobilised enzymes was observed after about 140 determinations in 14 d.