ISSN:
1573-6881
Keywords:
Ca2+ binding
;
Ca2+-Mg2+-ATPase
;
sarcoplasmic reticulum
;
cAMP
;
protein kinase
;
cooperativity
;
cardiac muscle
;
membrane protein
;
kinetics
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Physics
Notes:
Abstract Canine cardiac sarcoplasmic reticulum (SR) is known to be phosphorylated by adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase on a 22,000-dalton protein, Phosphorylation is associated with an increase in both the initial rate of Ca2+ uptake and the Ca2+-ATPase activity which is partially due to an increase in the affinity of the Ca2+-Mg2+-ATPase (E) of sarcoplasmic reticulum for calcium. In this study, the effect of cAMP-dependent protein kinase phosphorylation on the binding of calcium to the SR and on the dissociation of calcium from the SR was examined. The rate of dissociation of the E·Ca2 was measured directly and was not found to be significantly altered by cAMP-dependent protein kinase phosphorylation. Since the affinity of the enzyme for Ca2+ is equal to the ratio of the on and off rates of calcium, these results demonstrate that the observed change in affinity must be due to an increase in the rate of calcium binding to the Ca2+-Mg2+-ATPase of SR. In addition, an increase in the degree of positive cooperativity between the two calcium binding sites was associated with protein kinase phosphorylation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00743939
