Activation of alanine aminotransferase in serum by pyridoxal phosphate

Alanine aminotransferase activity in serum increases significantly when serum is incubated with pyridoxal phosphate. The increase depends on the L-alanine concentration in the final assay mixture, being greatest at 800 mmol/liter. Preincubation of 22 normal sera, in a 10:1 ratio with an 8.09 mmol/liter pyridoxal phosphate solution, resulted in an increase in the alanine aminotransferase activity from 10.5 +/- 4.9 U/liter (mean +/- SD) to 28.4 +/- 5.3 U/liter, an increase of 170%. The absolute amount of apoalanine aminotransferase is relatively constant over a wide range of enzyme activities.