Pyridoxal 5'-phosphate as an activator of the apoenzyme of alanine aminotransferase in human serum.

The relationship between reaction conditions and the stimulation of alanine aminotransferase by pyridoxal 5'-phosphate was investigated. Reaction conditions given for optimized alanine aminotransferase measurements are also optimal for measurements in the presence of pyridoxal 5'-phosphate taking into consideration the inhibitory effect of phosphate buffer. Addition of 150 mumol/1 pyridoxal 5'-phosphate to the reaction mixture guarantees a maximal stimulation after a pre-incubation period of 10 min. Factors influencing the magnitude of stimulation rates of both aminotransferases in different patient groups by pyridoxal 5'-phosphate are discussed.