Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The light microsomal fraction was isolated from homogenates of rabbit and bullfrog gastric mucosa. On examination with the electron microscope, the light microsomes appear as tubular membranous structures with morphology and dimensions similar to the elements of the smooth‐surfaced endoplasmic reticulum seen in intact oxyntic cells. A K<jats:sup>+</jats:sup>‐stimulated, Mg<jats:sup>++</jats:sup>‐requiring p‐nitrophenylphosphatase has been demonstrated in the gastric microsomes. Neither Na<jats:sup>+</jats:sup> nor ouabain (10<jats:sup>−6</jats:sup>–10<jats:sup>−3</jats:sup> M) altered the K<jats:sup>+</jats:sup>‐stimulated phosphatase. SCN<jats:sup>−</jats:sup> was not very effective as an inhibitor of the gastric microsomal phosphatase, in contrast to the effect of this anion on the ATPase activity; however, the gastric phosphatase as well as the ATPase are destroyed by phospholipase C, thus showing the lipoprotein nature of these enzymes. Kinetics of the K<jats:sup>+</jats:sup> activation of the microsomal phosphatase suggest that the K<jats:sup>+</jats:sup>‐PNPP complex is the active substrate for the enzymic reaction. Rb<jats:sup>+</jats:sup>, NH<jats:sub>4</jats:sub> <jats:sup>+</jats:sup> and Cs<jats:sup>+</jats:sup> will substitute to some degree for K<jats:sup>+</jats:sup> as an activator of the microsomal phosphatase. It is pointed out that K<jats:sup>+</jats:sup> is an essential requirement for HCl secretion in intact gastric mucosa and the replacement of K<jats:sup>+</jats:sup> with Rb<jats:sup>+</jats:sup>, Cs<jats:sup>+</jats:sup> and NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> is discussed. The K<jats:sup>+</jats:sup>‐stimulated phosphatase presented in this paper may play a role in the H<jats:sup>+</jats:sup> secretion process.</jats:p>