title: Ionic and substrate requirements of the high affinity calcium pumping ATPase in endoplasmic reticulum of pancreas.
abstract: 1. Calcium transport and ATPase activities were determined in microsomal vesicles from pancreatic tissue enriched in endoplasmic reticulum membranes. 2. Calcium transport and ATPase share the following properties: (i) magnesium was required with a K0.5 of 0.7 mM and maximal pumping ATPase activity at 5 mM Mg-ATP; (ii) at saturating magnesium concentrations, calcium increased ATP splitting activity up to three times with an apparent K0.5 close to 0.3 microM calcium; (iii) potassium stimulated the high calcium affinity Mg2+-dependent ATPase and calcium transport. 3. The properties of the calcium pumping system fulfil the cationic and substrate requirements from a physiological point of view.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008861:Microsomes / Q000378:metabolism; D010179:Pancreas / Q000201:enzymology*; D013347:Subcellular Fractions / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases; D002118:Calcium