+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Ionized and bound calcium inside isolated sarcoplasmic reticulum of skeletal muscle and its significance in phosphorylation of adenosine triphosphatase by orthophosphate

Ionized and bound calcium inside isolated sarcoplasmic reticulum of skeletal muscle and its significance in phosphorylation of adenosine triphosphatase by orthophosphate

European Journal of Biochemistry 97(1): 239-250

Calcium loading of skeletal muscle sarcoplasmic reticulum performed passively by incubation with high calcium concentrations (0.5--15 mM) on ice gives calcium loads of 50--60 nmol/mg sarcoplasmic reticulum protein. This accumulated calcium is not released by EGTA [ethyleneglycol bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid], but almost completely released by ionophore X-537A plus EGTA or phospholipase A plus EGTA treatment and is therefore assumed to be inside the sarcoplasmic reticulum. This calcium is distributed in one saturable and one non-saturable calcium compartment, as derived from the dependence of the calcium load on the calcium concentration in the medium. These compartments are assigned to bound and ionized calcium inside the sarcoplasmic reticulum, respectively. Maximum calcium binding under these conditions was 33 nmol/mg protein with an apparent half-saturation constant of 5,8 nmol/mg free calcium inside, or between 1.2 and 0.6 mM free calcium inside, assuming an average vesicular water space of 5 or 10 microliter/mg protein, respectively. Calcium-dependent phosphorylation of sarcoplasmic reticulum calcium-transport ATPase from orthophosphate depends on the square of free calcium inside, whilst inhibition of phosphorylation depends on the square of free calcium in the medium. Calcium-dependent phosphorylation appears to be determined by the free calcium concentrations inside or outside allowing calcium binding to the ATPase according to the two classes of calcium binding constants for low affinity calcium binding or high affinity calcium binding, respectively. It is further suggested that the saturation of the low-affinity calcium-binding sites of the ATPase facing the inside of the sarcoplasmic reticulum membrane is responsible for the greater apparent orthophosphate and magnesium affinity in calcium-dependent phosphorylation than in calcium-independent phosphorylation from orthophosphate. Maximum calcium-dependent phosphoprotein formation at 20 degrees C and pH 7.0 is about 4 nmol/mg sarcoplasmic reticulum protein.

Please choose payment method:

(PDF emailed within 0-6 h: $19.90)

Accession: 040505746

Download citation: RISBibTeXText

PMID: 157875

DOI: 10.1111/j.1432-1033.1979.tb13108.x

Related references

Tightly bound calcium of adenosine triphosphatase in sarcoplasmic reticulum from rabbit skeletal muscle. Journal of Biological Chemistry 255(23): 11351-6, 1980

Phosphorylation of the Calcium-Transport Adenosine Triphosphatase of Cardiac Sarcoplasmic Reticulum by Orthophosphate. Febs Journal 77(3): 611-619, 1977

Manganese as a cosubstrate for the phosphorylation of the sarcoplasmic reticulum Ca-dependent adenosine triphosphatase with orthophosphate. Biochimica Et Biophysica Acta. 1276(3): 188-194, 1996

Modulation in the rat skeletal muscle sarcoplasmic reticulum calcium adenosine triphosphatase transcripts following exercise training. Medicine & Science in Sports & Exercise 30(5 Suppl. ): S143, 1998

Studies on the structure of the calcium-dependent adenosine triphosphatase from rabbit skeletal muscle sarcoplasmic reticulum. Archives of Biochemistry and Biophysics 203(2): 780-791, 1980

Formation of magnesium-phosphoenzyme and magnesium-calcium-phosphoenzyme in the phosphorylation of adenosine triphosphatase by orthophosphate in sarcoplasmic reticulum. Models of a reaction sequence. European Journal of Biochemistry 119(2): 225-236, 1981

Effect of diethyl ether on the adenosine triphosphatase activity and the calcium uptake of fragmented sarcoplasmic reticulum of rabbit skeletal muscle. Journal of Biological Chemistry 242(20): 4637-4643, 1967

Association of chronic congestive heart failure in humans with an intrinsic upregulation in skeletal muscle sarcoplasmic reticulum calcium ion adenosine triphosphatase activity. American Journal of Cardiology 85(12): 1498-1500, 2000

Kinetic properties of calcium adenosine triphosphatase of sarcoplasmic reticulum isolated from cat skeletal muscles. A comparison of caudofemoralis (fast), tibialis (mixed), and soleus (slow). Journal of Biological Chemistry 254(21): 10675-8, 1979

Phosphorylation of the calcium-transport adenosine triphosphate of cardiac sarcoplasmic reticulum by orthophosphate. European Journal of Biochemistry 77(3): 611-619, 1977

Adenosine 5'-triphosphate modulation of catalytic intermediates of calcium-adenosine triphosphatase of sarcoplasmic reticulum subsequent to enzyme phosphorylation. Biochemistry 22(12): 2867-2875, 1983

Polymorphism of sarcoplasmic-reticulum adenosine triphosphatase of rabbit skeletal muscle. Biochemical Journal 197(1): 245-248, 1981

Enzyme phosphorylation with inorganic phosphate causes calcium dissociation from sarcoplasmic reticulum adenosine triphosphatase. Biochemistry 24(4): 922-925, 1985

Characterization of cardiac sarcoplasmic reticulum ATP-ADP phosphate exchange and phosphorylation of the calcium transport adenosine triphosphatase. European Journal of Biochemistry 64(1): 123-130, 1976

Roles of phosphorylation and nucleotide binding domains in calcium transport by sarcoplasmic reticulum adenosine triphosphatase. Biochemistry 27(16): 5885-5890, 1988