The modulation of Ca2+ binding to sarcoplasmic reticulum ATPase by ATP analogues is pH-dependent.
Excess ATP is known to enhance Ca(2+)-ATPase activity and, among other effects, to accelerate the Ca2+ binding reaction. In previous work, we studied the pH dependence of this reaction and proposed a 3H+/2Ca2+ exchange at the transport sites, in agreement with the H+/Ca2+ counter transport. Here we studied the effect of ADP and nonhydrolyzable ATP analogues on the Ca2+ binding reaction at various pH values. At pH 6, where Ca2+ binding is monophasic and slow, ADP, adenosine 5'-(beta,gamma-methylene)triphosphate (AMP-PCP), or adenyl-5'-yl imidodiphosphate (AMPPNP) increased the Ca2+ binding rate constant 20-fold. At pH 7 and 8, where Ca2+ binding is biphasic, the nucleotides induce fast and monophasic Ca2+ binding. At pH 7, AMP-PCP accelerated Ca2+ binding with an apparent dissociation constant of 10 microM. At acidic pH, ADP, AMPPCP, or AMPPNP increased the equilibrium affinity of Ca2+ for ATPase, whereas at alkaline pH, these nucleotides had no effect. At pH 5.5, AMPPCP increased equilibrium Ca2+ binding with an apparent dissociation constant of 1 microM.
Mintz
E
E
Département de Biologie Cellulaire et Moléculaire, Centre d'Etudes de Saclay, Gif-sur-Yvette, France.
Mata
A M
AM
Forge
V
V
Passafiume
M
M
Guillain
F
F
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D011522:Protons; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*
D011522:Protons; D000266:Adenylyl Imidodiphosphate; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium