[Changes in enzymes during aging of human diploid cells. Glucose-6-phosphate dehydrogenase]

The thermal inactivation kinetics of glucose-6-phosphate dehydrogenase during ageing of human diploid cells were studied. It was shown that semi-logarithmic anamorphisms of the thermal inactivation kinetic curves may be presented as a total of two rectilinear sites corresponding to the thermolabile and thermostable fractions of the enzyme. In ageing cells the enzyme stability is decreased as compared to the young ones due to the increase in the amount of the thermolabile fraction. It was also found that despite a certain variability in the process of the cell growth at the 22nd passage the thermal stability of glucose-6-phosphate dehydrogenase is decreased, while the enzyme thermal stability in the cells at the 52nd passage is monotonously increased. Purification of the enzyme from ageing and young human diploid cells results in an increase of the enzyme stability. However, when the enzyme was isolated from young cells, it possessed a higher thermal stability.