Determination of the activity of aminotransferases: comparison of two buffer systems with and without supplementary pyridoxal-5'-phosphate.

A comparison was made between the aminotransferase activities of a number of plasma or serum samples in 4 reaction media: phosphate buffer, phosphate buffer + pyridoxal-5'-phosphate, tris buffer and tris buffer + pyridoxal-5'-phosphate. The reactions were carried out in the various buffer systems on the same day at 35 degrees C on an automatic kinetic enzyme system (AKES, Vitatron, Dieren, the Netherlands). The highest enzymic activity of both aminotransferases is observed in tris buffer + pyridoxal-5'-phosphate. The activity is about 10--15% higher than in phosphate buffer + pyridoxal-5'-phosphate. Without supplementary pyridoxal-5'-phosphate the differences between both buffer systems are lower or absent. It appears necessary, therefore, to determine the activity of both aminotransferases in a buffer system with tris and to add pyridoxal-5'-phosphate, since assays should be carried out in the presence of optimal concentrations of any of the necessary factors.