An ecto-ATPase of thyroidal cell membrane.

Abstract

The isolated cells were obtained from hog thyroid glands treated with dispase. More than 95 % of the cells obtained were intact and viable immediately after preparation, and the cell viability did not change during incubation in the experimental conditions. ATP added to the external medium of whole cell suspensions was hydrolyzed in the presence of various divalent cations, especially Mg, and the rate of hydrolysis of ATP was not significantly different between the Mg-ion system and the completed ion system (Mg+ Na +K). When whole cell suspensions were disrupted with homogenizer, the hydrolysis of ATP was markedley increased by adding Na plus K. But there was no difference in the Mg-ion system between cell homogenates and whole cell suspensions.ADP, AMP and adenosine as reaction products were found in the reaction mixture which resulted from the hydrolysis of ATP by whole cell suspensions.Our data suggest that Mg-ATPase in the thyroidal isolated cells is an ectoenzyme whose active site(s) are exposed to the external surface of plasma membrane, and that ATP is finally hydrolyzed to adenosine via ADP and AMP by the enzyme(s).

Blood-brain barrier Ca2+-ATPase cytochemistry: incubation media and fixation methods for differentiating Ca2+-specific ATPase from ecto-ATPase

“…The ecto-ATPase has its active site exposed to the external surface of the plasma membrane (Yoshimura et al 1983, Lin and Russell 1988, Dombrowski et al 1993, Hohmann et al 1993, Smith et al 1999. In our study, the abluminal localization…”