Abstract
Effect of temperature on the Ca2+ transport ATPase of sarcoplasmic reticulum
Highlights
The effect of temperature on sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle was studied by measuring the Ca2+ uptake, ATP and ITP hydrolysis, Ca2+ efflux, ATP synthesis, ATP - Pi exchange reaction, and phosphorylation of the Ca 2+ transport enzyme by either ATP, ITP, or inorganic phosphate
The data presented support the concept of two different conformations of the Ca2+ transport enzyme in equilibrium and indicate that this equilibrium is modified by temperature
Evidence has been presented that the calcium is released into the lumen of the vesicles before hydrolysis of the phosphoenzyme
Summary
The effect of temperature on sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle was studied by measuring the Ca2+ uptake, ATP and ITP hydrolysis, Ca2+ efflux, ATP synthesis, ATP - Pi exchange reaction, and phosphorylation of the Ca 2+ transport enzyme by either ATP, ITP, or inorganic phosphate. When ITP is used as substrate, the increment of Pi liberation is accompanied by a decrease of the steady state level of phosphoenzyme This is not observed when ATP is used as substrate. Synthesis of ATP coupled to calcium efflux and ATP -+ Pi exchange reaction are inhibited at 0” Both the phosphorylation of the enzyme by P, and the transfer of phosphate from the phosphoenzyme to ADP are impaired at 0”. After hydrolysis ofE-P, the enzyme must undergo a new transition to transpose the Ca2+ binding
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