Structural and enzymic aspects of the hydrolysis of adenosine triphosphate by membranes of kidney cortex and erythrocytes

Publisher Website
Google Scholar
Abstract
The effects of some inhibitors of various membrane and other cellular processes on Na+ ion-plus-K+ ion-dependent adenosine-triphosphatase activity have been investigated by using a cell-debris fraction from rabbit kidney-cortex homogenate. This component of the enzymic activity was selectively inhibited by ouabain and also by Ca2+ ions, phlorrhizin, phloretin and oligomycin. The thiol reagent p-chloromercuribenzoate preferentially inhibited this component but, like N-ethylmaleimide, also inhibited that part of the adenosine-triphosphatase activity which was not dependent on Na+ and K+ ions. The distribution of the enzymic activity among subcellular fractions of kidney-cortex homogenate was determined and its association with membrane-containing fractions examined. The enzymic activity was distributed mainly between the cell-debris and microsomal fractions. A crude membrane fraction showed the highest proportion of Na+ ion-plus-K+ ion-dependent activity, whereas a more purified fraction contained only a small proportion of this component. A partial frac-tionation of human erythrocyte membranes was attempted by monitoring the adenosine-triphosphatase activity of the material obtained during the various stages in the isolation of the main lipoprotein component of the membranes. The activity dependent on Na+ and K+ ions was lost during the procedures involving solubilization and salting out at alkaline pH. Evidence is presented that the Na+ ion-plus-K+ ion-dependent adenosine-triphosphatase activity is essentially a membrane enzyme system and is probably involved in membrane transport phenomena.