Laboratory  of  John G. Forte

Department of Cell & Molecular Biology,  University of California, Berkeley
 
  JOURNAL OF CELLULAR PHYSIOLOGY, Vol. 69, No. 3, 293-304, June 1967
 

K+-stimulated Phosphatase of Microsomes from Gastric Mucosa
  John G. Forte, Gerturde M. Forte, and Paul Saltman
Department of Physiology, University of California, Berkeley, California, and The Graduate Program in Biochemistry, University of Southern California, Los Angeles, California 		 

 

  Abstract: 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+-stimulated, Mg++-requiring p-nitrophenylphosphatase has been demonstrated in the gastric microsomes. Neither Na+ nor ouabain (10-6-10-3 M) altered the K+-stimulated phosphatase.  SCN- was not very effective as an inhibitor of 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+ activation of the microsomal phosphatase suggest that the K+-pNPP complex is the active substrate for the enzymic reaction. Rb+, NH4+ and Ca++ will substitute to some degree for K+ as an activator of the microsomal phosphatase. It is pointed out that K+ is an essential requirement for HCl secretion in intact gastric mucosa and the replacement of K+ with Rb+, Ca++ and NH4+ is discussed. The K+-stimulated phosphatase presented in this paper may play a role in the H+ secretion process.