title: Effect of calcium and magnesium on binding of beta, gamma-methylene ATP to sarcoplasmic reticulum.
abstract: Isolated sarcotubular membranes (SR) from skeletal muscle bound 3.7 nmol of beta, gamma-methylene [8-3H]ATP (AMP-PCP) per mg of membrane protein. Only one class of binding site was identified and the dissociation constant (K) for this site was 1.5 X 10(-5) M. Addition of 0.05% Triton X-100 increased the number of binding sites to 5.7 nmol/mg. ATP and ADP competitively inhibited AMP-PCP binding. The dissociation constants for ATP and ADP were 3.5 X 10(-5) M and 3.3 X 10(-6) M, respectively. Since this data was obtained in the presence of 5 mM EDTA, it was established that the sarcoplasmic reticulum has a high affinity for the metal free forms of ATP, ADP, and AMP-PCP. Magnesium concentrations in excess of 1 X 10(-4) M inhibited AMP-PCP binding. Lower concentrations of magnesium had little effect on AMP-PCP binding. The effect of calcium on AMP-PCP binding was biphasic. Calcium concentration between 1 X 10(-6) and 1 X 10(-4) M inhibited AMP-PCP binding. Inhibition was maximal at 1 X 10(-5) M. Calcium concentration above 1 X 10(-4) M facilitated analogue binding. Possible sites of magnesium and calcium actions are discussed.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D009711:Nucleotides / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D009711:Nucleotides; D011092:Polyethylene Glycols; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium