Frog Gastric Mucosal ATPase.

Abstract

In recent years interest in extramitochon-drial ATPases has centered in large part on ‘transport' ATPases. These enzymes have been prepared from a variety of tissue—such as crab nerve(l), red blood cells(2), kidney (3), rat brain(4), and other tissues(5). They share a certain number of features in common, namely a stimulation by Na+ and K+ and at least partial inhibition by ouabain. Furthermore, in the standard cellular fractionation methods, the ouabain-inhibitable Na+ and K+ sensitive component occurs in the microsomal fraction which is considered to contain a large proportion of fragmented membrane. Further evidence for the involvement of the microsomal fraction in transport involves (a) ATP-dependent Na+ binding to the protein of brain microsomes (4); (b) P32 labelling of protein derived from ATP32 in r.b.c. membranes(6) and (c) the reduction of labelled phosphoserine from kidney ATPase preparations incubated with DFP32 in the presence of ATP and a possible identity of this ATPase and diglyceride kinase(7). The gastric mucosa under normal conditions apparently contains at least 2 electrogenic pumps acting on Cl- and H+ respectively (8). The specificity of the pumps in the gastric mucosa may make it extremely difficult to characterize a ‘pump’ ATPase in the same manner as has been done for those described above. Thus the chloride mechanism has been shown to transport several univalent anions in the mucosa and to have some action on sulfate(9). Therefore the anion pump may be regarded as relatively nonspecific. The hydrogen ion pump is apparently specific for H+. A demonstration of H+ activation is naturally complicated by the pH activity curves obtained for enzymic reactions. The evidence therefore for a hydrogen ion pump must at present rest on the action of specific inhibitors.