Cyclic AMP stimulation of membrane phosphorylation and Ca2+-activated, Mg2+-dependent ATPase in cardiac sarcoplasmic reticulum

1977 ◽  
Vol 461 (3) ◽  
pp. 441-459 ◽  
Author(s):  
H.Linton Wray ◽  
R.Richard Gray
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cyclic Amp ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Dependent Atpase ◽  
Membrane Phosphorylation ◽  
Stimulation Of

scholarly journals Effect of cyclic AMP-dependent phosphorylation on the reactivity of sulphydryl groups in cardiac sarcoplasmic reticulum

1980 ◽  
Vol 192 (3) ◽  
pp. 867-872 ◽  
Author(s):  
C J Limas
Keyword(s):  
Protein Kinase ◽  
Sarcoplasmic Reticulum ◽  
Cyclic Amp ◽  
Thiol Groups ◽  
Dependent Protein Kinase ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Dependent Atpase ◽  
Dependent Protein ◽  
Sulphydryl Groups ◽  
Atpase Inhibition

Phosphorylation of cardiac sarcoplasmic reticulum by cyclic AMP-dependent protein kinase results in enhanced Ca2+ transport even though Ca2+-dependent ATPase is not a substrate for the kinase. The mechanisms involved in this enhancement are not clear. In the present study, we used the reactivity of sulphydryl groups in the Ca2+-dependent ATPase as an index of conformational change during the Ca2+ transport cycle and examined the effects of protein kinase-catalysed phosphorylation. N-Ethylmaleimide alkylation allowed the distinction of several thiol groups with variable functional significance for the ATPase. A sulphydryl group involved in the formation of the phosphorylated intermediate (EP) of the Ca2+-dependent ATPase was protected by adenosine 5′-[beta, gamma-imido]triphosphate. Reactivity of an additional thiol group was related to EP dephosphorylation and was dependent on Ca2+. The Ca2+ concentration for change in the reactivity of this sulphydryl group and ATPase inhibition occurred within the range for Ca2+ binding to the high-affinity sites. Phosphorylation of cardiac sarcoplasmic reticulum by cyclic AMP-dependent protein kinase resulted in decreased N-ethyl[1-14C]-maleimide binding and the ATPase inhibition; the thiol groups involved in EP dephosphorylation were selectively protected. The results indicate that protein kinase-catalysed phosphorylation results in conformational changes of the ATPase, which renders certain thiol groups inaccessible to N-ethylmaleimide. This conformational change may facilitate functional movements involved in Ca2+ transport.

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