Increased aspartate aminotransferase activity of serum after in vitro supplementation with pyridoxal phosphate.

We examined the effect of pyridoxal phosphate supplementation on the apparent aspartate aminotransferase (EC 2.6.1.1.) activity of human serum. Supplementation by 25 mol/liter effected an average increase of 16% in the results for kinetic assay. The increase was not the result of increased enzymatic or nonenzymatic blanks, and, within a small range, sample dilution had no significant effect. Part of the increase was attributableto the enzyme being protected against the loss of activity that occurs during preincubation with L-aspartate. A similar increase was not demonstrated in a two-point colorimetric method, perhaps because of the short reaction time, without preincubation, and the initialpresence of both substrates in the assay. We attempted to Correlate such stimulation of aminotransferase activity and the patient’s diagnosis or treatment. Pyridoxal phosphate should be included in the reaction mixture when aspartate aminotransferase activity is being measured clinically.