Effects of polycations on Ca2+ binding to the Ca(2+)-ATPase.
Spermine and polyarginine have been shown to increase the rate of dissociation of Ca2+ from the Ca(2+)-ATPase of skeletal-muscle sarcoplasmic reticulum. They also decrease the affinity of the ATPase for Mg2+ as detected by changes in the fluorescence intensity of the ATPase labelled with 4-(bromomethyl)-6,7-dimethoxycoumarin (DMC). Polyarginine itself also decreases the fluorescence intensity of DMC-labelled ATPase. These results are consistent with binding of spermine and polyarginine to a gating site controlling the rate of access of Ca2+ to its binding sites on the ATPase. A basic peptide PLN-(1-25) corresponding to residues 1-25 of phospholamban had no effect on the rate of dissociation of Ca2+ or on the fluorescence of DMC-labelled ATPase. Spermine, polyarginine and PLN-(1-25) all increased the equilibrium constant E1/E2, and spermine and polyarginine increased the rate of Ca2+ binding to the ATPase, consistent with an increase in the rate of the E2-->E1 transition. Spermine displaced Tb3+ and Ruthenium Red from the ATPase, consistent with binding in the stalk region of the ATPase. Polyarginine and PLN-(1-25), however, had no effect on Tb3+ or Ruthenium Red binding, suggesting a greater specificity in binding basic peptides to the ATPase than spermine.
Hughes
G
G
Department of Biochemistry, University of Southampton, U.K.
Khan
Y M
YM
East
J M
JM
Lee
A G
AG
D000595:Amino Acid Sequence; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011073:Polyamines / Q000737:chemistry; D000071228:Polyelectrolytes; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013096:Spermine / Q000737:chemistry; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D010455:Peptides; D011073:Polyamines; D000071228:Polyelectrolytes; D013096:Spermine; D000099211:Phospholamban; C015462:polyarginine