Thyroid Gland Ecto-ATPase and Some of Its Kinetic Properties

Plasma membrane of human thyroid gland, apart from the transport Mg-independent HCO₃^—ATPase, has been found to contain also HCO₃^--ATPase of ecto-ATPase type, whose activity is not conditioned by the Mg-ion and with substrate in the form of free ATP (ecto-HCO₃^--ATPase). Activity of such kind is found in both healthy cells and those affected by carcinoma. However, in the latter cells, this characteristic of the enzyme is much higher than the norm. We studied certain kinetic properties of the Mg-independent HCO₃^--ATPase, namely relation of its activity to the quantitative content of the HCO ₃^--ions and the substrate (free ATP), as well as the pH of the reaction medium. Experiments showed that properties of ecto-HCO₃^--ATPase are different from those of Mg-HCO₃^--ATPase, which allows for a conclusion that the two enzymes can function independently and are involved in different processes in progress in thyroid gland cells.