Ionic and substrate requirements of the high affinity calcium pumping ATPase in endoplasmic reticulum of pancreas.
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.
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
D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases; D002118:Calcium