Aspartate Aminotransferase Assay
Method: Aspartate aminotransferase may be assayed spectrophotometrically in a coupled reaction with malate dehydrogenase in the presence of NADH (Karmen 1955; Amador and Wacker 1962). One unit oxidizes one micromole of NADH per minute at 25°C and pH 7.4 under the specified conditions.
Prepare reagent mixture containing:
Dissolve enzyme at a concentration of one mg/ml in 0.1 M potassium phosphate pH 7.4. Immediately prior to use, dilute further in this buffer to a concentration of 0.05 - 0.25 u/ml.
Adjust spectrophotometer to 340 nm and 25°C. Pipette 2.9 ml of the reagent mixture into cuvette and place in spectrophotometer. Incubate for 3 - 4 minutes to reach temperature equilibrium and establish blank rate, if any. At zero time, add 0.1 ml of apropriately diluted enzyme and record the decrease in A340 for 4 - 5 minutes. Calculate ΔA340/minute from the initial linear portion of the curve.