BIOCHIMICA ET BIOPHYSICA ACTA 293 BBA 75 998 THE PRESENCE OF A HCO3--ATPase IN PANCREATIC TISSUE B. SIMON, R. KINNE AND G. SACHS* University of Alabama Medical Center, Birmingham, Ala. (U.S.A.), and Max Planck Institut far Biophysik, Frankfurt a. M (Germany) (Received February 29th, I972) SUMMARY An ATPase was isolated and partially purified from mammalian pancreas. It was shown to be stimulated several fold by HC0a- and other anions, and to be completely inhibited by SCN- and CNO-. In many of its properties it resembles gastric ATPase and a model is suggested to account for pancreatic HCO 3- secretion. INTRODUCTION Recently it has proved possible to further characterize an ATPase from gastric mucosal, ~, stimulated by HCO 3- and inhibited by SCN- (refs 3, 5)- Summarizing our findings: (a) This enzyme is localized in the acid secreting cell of the mucosa. (b) It is localized in a smooth membrane vesicular fraction of that cell banding between 1.o9 and 1.12 density in a sucros~gradient. (c) It is solubilized byTriton X-Ioo, and can be further purified on a Sephadex G-2oo column and 2 to 22 % sucrose density gradient. (d) A variety of bases can stimulate the enzyme, such as arsenate, sulfite, etc. as a function of the pK of the base. (e) The enzyme can be distinguished from mito- chondrial ATPase because of location of this enzyme and mitochondrial markers such as succinate dehydrogenase and monamine oxidase on the density gradient. (f) A variety of inhibitors has been found for this enzyme such as SCN-, CN0-, NO~-, etc. which all inhibit acid secretion (G. Sachs, unpublished results). In short, the various properties have been interpreted to mean that this enzyme is involved in some critical phase of acid secretion and two types of model have been suggested, based on Mit- chell's e ATPase I model or on a coupled redox-ATPase model where the ATPase provides the necessary vectorialization. Since the pancreas is known to secrete HCO~- actively7, it seemed likely that a similar type of enzyme might be involved in this process, and with some differences in detail, this has been shown for pancreas from dog or cat. Hence a model is proposed for active HCO.~- secretion by this organ. METHODS AND MATERIALS Preparation of membrane-bound HCO3--A TPase Dog or cat pancreatic tissue was freed of fat and adjacent connective tissue, * To whom correspondence should be addressed. Biochim. Biophys. Acta, 282 (i972) 293-3oo