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CaATP: the substrate, at low ATP concentrations, of Ca2+ ATPase from human erythrocyte membranes. 1981

E Graf, and J T Penniston

Detailed kinetic analyses of ATP-splitting activities were obtained with purified Ca2+ ATPase from human erythrocyte membranes. At constant low total ATP levels increasing Mg2+ inhibited the activity of the enzyme, while increasing Ca2+ did not. Detailed analysis of this phenomenon with appropriate controls showed that this occurred because Ca2+ . ATP4- (CaATP) was the substrate for the enzyme: the inhibition by Mg2+ was due to the lowering of the CaATP concentration as Mg2+ replaced Ca2+ as the metal bound to ATP. Free ATP could not be the substrate, since its concentration could be lowered by increasing total Ca2+, and no inhibition of the reaction occurred. In addition to this site for CaATP, the enzyme may contain yet another metal-ATP site of much lower affinity and less specificity with respect to the metal. The data also indicate the presence of a Mg2+ site and a Ca2+ site in addition to the CaATP site. Since the enzyme also interacts with calmodulin, it effectively interacts with Ca2+ at three sites: the Ca2+ site, the CaATP site, and the Can-calmodulin site. The enzyme displays the same characteristics in the presence of calmodulin. However, the stimulation by calmodulin is always about three times higher in the presence of Mg2+ than in its absence. A model for the mechanism of this enzyme is discussed.

UI MeSH Term Description Entries
D007700 Kinetics The rate dynamics in chemical or physical systems.
D008274 Magnesium A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D008433 Mathematics The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed) Mathematic
D002118 Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D004910 Erythrocyte Membrane The semi-permeable outer structure of a red blood cell. It is known as a red cell 'ghost' after HEMOLYSIS. Erythrocyte Ghost,Red Cell Cytoskeleton,Red Cell Ghost,Erythrocyte Cytoskeleton,Cytoskeleton, Erythrocyte,Cytoskeleton, Red Cell,Erythrocyte Cytoskeletons,Erythrocyte Ghosts,Erythrocyte Membranes,Ghost, Erythrocyte,Ghost, Red Cell,Membrane, Erythrocyte,Red Cell Cytoskeletons,Red Cell Ghosts
D004912 Erythrocytes Red blood cells. Mature erythrocytes are non-nucleated, biconcave disks containing HEMOGLOBIN whose function is to transport OXYGEN. Blood Cells, Red,Blood Corpuscles, Red,Red Blood Cells,Red Blood Corpuscles,Blood Cell, Red,Blood Corpuscle, Red,Erythrocyte,Red Blood Cell,Red Blood Corpuscle
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000252 Calcium-Transporting ATPases Cation-transporting proteins that utilize the energy of ATP hydrolysis for the transport of CALCIUM. They differ from CALCIUM CHANNELS which allow calcium to pass through a membrane without the use of energy. ATPase, Calcium,Adenosinetriphosphatase, Calcium,Ca(2+)-Transporting ATPase,Calcium ATPase,Calcium Adenosinetriphosphatase,Adenosine Triphosphatase, Calcium,Ca2+ ATPase,Calcium-ATPase,ATPase, Ca2+,ATPases, Calcium-Transporting,Calcium Adenosine Triphosphatase,Calcium Transporting ATPases,Triphosphatase, Calcium Adenosine
D000255 Adenosine Triphosphate An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter. ATP,Adenosine Triphosphate, Calcium Salt,Adenosine Triphosphate, Chromium Salt,Adenosine Triphosphate, Magnesium Salt,Adenosine Triphosphate, Manganese Salt,Adenylpyrophosphate,CaATP,CrATP,Manganese Adenosine Triphosphate,MgATP,MnATP,ATP-MgCl2,Adenosine Triphosphate, Chromium Ammonium Salt,Adenosine Triphosphate, Magnesium Chloride,Atriphos,Chromium Adenosine Triphosphate,Cr(H2O)4 ATP,Magnesium Adenosine Triphosphate,Striadyne,ATP MgCl2

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