title: ATP-dependent calcium sequestration and calcium/ATP stoichiometry in isolated microsomes from guinea pig parotid glands.
abstract: ATP-dependent calcium uptake was studied in isolated guinea pig parotid gland microsomes. The apparent Km for free Ca2+ was 0.41, microM, the apparent Km for ATP X Mg2- 0.23 mM. The pH optimum was 6.8-7.0. Subfractionation of the microsomes revealed that the highest specific uptake activity resided in a rather dense fraction of the endoplasmic reticulum. The calcium uptake/ATPase stoichiometry was determined in the absence of exogenous magnesium in the submicrosomal fractions. It ranged from 1-2. It is concluded that in vivo the stoichiometry is the same as in sarcoplasmic reticulum, namely 2.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D008861:Microsomes / Q000378:metabolism; D010070:Oxalates / Q000502:physiology; D019815:Oxalic Acid; D010306:Parotid Gland / Q000378:metabolism*
chemical_list: D010070:Oxalates; D000255:Adenosine Triphosphate; D019815:Oxalic Acid; D000251:Adenosine Triphosphatases; D002118:Calcium