Occurrence and characteristics of a rapid exchange of phosphate oxygens catalyzed by sarcoplasmic reticulum vesicles
Sarcoplasmic reticulum vesicles prepared from rabbit skeletal muscle catalyze a rapid P{subi} {l_reversible} HOH exchange in the presence of Mg++ and absence of ATP and Ca++. The capacity for oxygen exchange is about fourteen times the potential capacity for ATP cleavage in the presence of Ca++. No detectable exchange is found without added MgC1{sub2}. The exchange is unaffected by oligomycin, 2,4-dinitrophenol or ouabain, but strongly inhibited by low concentrations of Ca++ in the medium. The Ca++ ion concentration giving a half-maximum inhibition is 2.0 {mu}M in the presence of 5 mM MgC1{sub2}. A Hill plot of the Ca++ inhibition gives a straight line with a Hill coefficient of 1.8. The Ca++ inhibition is competitively overcome by additional Mg++. The P{subi} {l_reversible} HOH exchange is almost completely inhibited by the detergent Triton X-100 at low concentrations where the ATPase activity is not disturbed. Sarcoplasmic reticulum vesicles are phosphorylated by P{subi} in the presence of Mg++ and absence of Ca++ under conditions similar to those for the P{subi} {l_reversible} HOH exchange. The phosphorylation requires Mg++ and is strongly inhibited by low concentrations of Ca++. The response of the phosphorylation to Ca++ is quite similar to that of the P{subi} {l_reversible} HOH exchange; the Ca++ ion concentration giving a half-maximum inhibition is 2.0 {mu}M in the presence of 5 mM MgC1{sub2} and the Hill coefficient is about 2.0. The various properties of the exchange give strong support to the probability that it results from reversal of steps in the overall process associated with CA++ transport driven by ATP cleavage.
- Research Organization:
- University of California, Los Angeles (USA)
- Sponsoring Organization:
- U.S. Atomic Energy Commission (AEC)
- DOE Contract Number:
- AT(04-3)-34
- NSA Number:
- NSA-28-015168
- OSTI ID:
- 4473783
- Report Number(s):
- UCLA--34-P-102-35
- Country of Publication:
- United States
- Language:
- English
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