title: Effect of pH on stability of sarcoplasmic reticulum calcium pump in rabbit heart.
abstract: The sarcoplasmic reticulum (SR) membranes isolated from rabbit heart were preincubated at pH 6.8 or 7.8 and their Ca2+ pump properties were compared at pH 6.8. The ATP-dependent azide insensitive oxalate-stimulated Ca2+ uptake was reduced more rapidly from the membranes preincubated at 37 degrees C at pH 7.8 than from those preincubated at pH 6.8. The Ca(2+)-Mg(2+)-ATPase, and the Ca(2+)-dependent formation of 110 kDa acylphosphate were also inhibited by the preincubation at the higher pH. Including 1 mM DTT in the preincubation medium reduced the inactivation. The preincubation at 37 degrees C in the presence or absence of DTT caused membranes to become more leaky as the loss of Ca2+ uptake was more rapid than that of ATPase or the acylphosphate formation. The loss of these activities was not accompanied by a breakdown of the protein as monitored in Western blots. It is hypothesized that the SR Ca2+ pump inactivation involves a key-SH group and that the lower pH provides a compensatory protective mechanism for the SR during acidosis.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Xu
authors.forename: N
authors.initials: N
authors.lastname: Narayanan
authors.forename: S E
authors.initials: SE
authors.lastname: Samson
authors.forename: A K
authors.initials: AK
authors.lastname: Grover
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D000252:Calcium-Transporting ATPases