Abstract

It has been shown that heat inactivation of L-threonine- and L-serine dehydratase activities at 37; 45; 50 and 55 degrees C in human liver extracts (the liver was ectracted with buffer containing 1.10(-5) M of pyridoxal 5'-phosphate) in course of time is practically identical, and characterizes by the same of values of activation energy of heat inactivation process, activation enthalpy of this process, activation free energy of that and activation enthalpy of the heat inactivation process. A rise of pyridoxal 5'-phosphate concentration (to 2.10(-4) M) in the buffer used for the liver extraction and hence in the medium in which the heat inactivation process was carried out stabilises L-threonine- and L-serine dehydratase activities against the inactivation at 55 degrees C. It has been concluded thatL-threonine- and L-serine dehydratase activities in human liver belong to the single protein or to two proteins having very like physico-chemical properties, and that pyridoxal 5'-phosphate is essential for this enzyme not only as coenzyme but also it is necessary to support active and stable conformation of this oligomeric protein.