Adult and fetal galactokinases in human red blood cells

This paper reports the biochemical properties of galactokinase from fetal and adult human red blood cells. The specific activity of galactokinase is three times higher in the fetal red cells than in adult cells, shows a significant difference in the Michaelis constant toward galactose, and is more thermostable. On the other hand, no differences were found in molecular weight, electric charge, temperature and pH dependence between the two enzymes partly purified from fetal and adult erythrocytes. The possibility that these differences could be due to the shorter lifespan of the fetal erythrocytes (which could result in a higher proportion of young cells in the blood samples utilized) was investigated. Fetal and adult red blood cells were separated into fractions of different mean age by ultracentrifugation through density gradients. The kinetic properties and thermostability of galactokinase from fetal erythrocytes do not show any similarity with the same properties of the enzyme from young red blood cells. These results indicate that galactokinase from fetal erythrocytes show some biochemical properties that are typical signs distinguishing a fetal enzyme.