Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The parameters of the hydrolysis of ATP and several analogs by soluble mitochondrial ATPase were determined. Vmax of the reaction decreases within the range: 2'-desoxy-ATP greater than ATP greater than etheno-ATP greater than GTP greater than 3'-O-methylATP greater than UTP. ATP, 2'-desoxypATP, 3'O-methyl-ATP, GTP, and etheno-ATP are hydrolysed by soluble mitochondrial ATPase with close Km(app) values. CTP is not hydrolysed by the enzyme and does not inhibit the ATPase reaction at a concentration of 10(-2) M. Nucleoside triphosphate derivatives with an "open" ribose cycle 9-[1',5'-dihydroxy-4-(S)-hydroxymethyl-3'-oxapent-2' (R)-yl]adenyl-5'-triphosphate, and 1-[1',5'-dihydroxy-4'-(S)-hydroxymethyl-3'-oxapent-2'(R)-yl[cytosine-5'-triphosphate are effective inhibitors of ATPase (Ki approximately 5.10(-5)M). Mitochondrial ATPase binds the ATP analogs that have hydrocarbon radicals-(CH2)2-, -(CH2)3-, and (CH2)4- instead of the ribose residues: 9-(2'hydroxyethyl)adenyl-2'-triphosphate, 9-(3'-hydroxypropyl)-adenine-3'-triphosphate, and 9-(4'-hydroxybutyl)adenine-4'-triphosphyl)adenine-4'-triphosphate were not hydrolysed by the enzyme, although they inbibit the ATPase reaction (Ki 2.10(-4)M). 9-(2'-hydroxyethyl)adenine-2'-triphosphate is hydrolysed by ATPase eight times more slowly than ATP. It is suggested that the hydrolysis of the substrates of mitochondrial ATPase is- preceded by the binding of the substrates in a tense conformation in the active site of the enzyme.
 ...
PMID:[Substrate specificity of soluble mitochondrial ATPase]. 14 22

An increase in pH decreases the Na+ concentration (Na+ +K+ = 150 mM) necessary for half-maximum activation of the (Na+ +K+)-ATPase at non-saturating concentrations of ATP just as an increase in the concentration of ATP at a given pH. It also decreases the concentration of Na+ necessary for transformation from the K+-form to the Na+-form at equilibrium conditions (Na+ +K+ = 150 mM). An increase in pH increases the rate of the transformation from the K+-form to the Na+-form of the system and decreases the rate of the reverse reaction. The pH effect on the conformation suggests that the K+-form is a protonated form and the Na+-form a deprotonated one. The similarity between the effect of an increase in pH with non-saturating concentrations of ATP and that of an increase in ATP at a given pH suggests that ATP exerts its effect on the transformation from the K+ - to the Na+-form by a decrease in pK values of the system, i.e., by releasing protons, a Bohr effect. Enzyme modified by reaction with pyridoxal 5-phosphate terminated by NaBH4 behaves at a given pH as if it were non-modified enzyme but at a higher pH. The 'pH effect' is seen after modification by pyridoxal 5-phosphate in the presence of ATP, of Na+ without and with ATP, of K+ with ATP but not in the presence of K+ alone. The modification has also a 'pH effect' on the rate of the transformation from the K+ -form to the Na+ -form and on the reverse reaction. There are at least two different pyridoxal 5-phosphate-reactive groups (amino groups), one which can be protected by ATP and which is of importance for activity and another which is not protected by ATP and which is of importance for the pH effect on the conformation. The effect of a protonation-deprotonation of amino groups on the conformation is explained by an involvement of the amino groups in salt bridge formation in between and inside the polypeptide chains, a hemoglobin-like situation. The protonated K+ -form is then a tense T-structure with a high K+, low Na+ affinity and the deprotonated Na+ -form a relaxed, R-structure with high Na+, low K+ affinity. ATP facilitates deprotonation by decreasing pK values. Oligomycin has 'pH effect' on the K0.5 for Na+ under equilibrium and steady-state conditions, but oligomycin has no effect on the rate of the transformation from the K+ -form to the Na+ -form, but gives a pronounced decrease of the rate of the reverse reaction, indicating that oligomycin does not react with the K+ -form but with the Na+ -form of the system and prevents the protonation, the E1 to E2 transformation.
 ...
PMID:The effect of pH, of ATP and of modification with pyridoxal 5-phosphate on the conformational transition between the Na+-form and the K+-form of the (Na+ +K+)-ATPase. 628 65

Phosphorylation by protein kinase A and dephosphorylation by protein phosphatase 1 modulate the inhibitory activity of phospholamban (PLN), the endogenous regulator of the sarco(endo)plasmic reticulum calcium Ca(2+) ATPase (SERCA). This cyclic mechanism constitutes the driving force for calcium reuptake from the cytoplasm into the myocite lumen, regulating cardiac contractility. PLN undergoes a conformational transition between a relaxed (R) and tense (T) state, an equilibrium perturbed by the addition of SERCA. Here, we show that the single phosphoryl transfer at Ser16 induces a more pronounced conformational switch to the R state in phosphorylated PLN (pPLN). The binding affinity of PLN to SERCA is not affected (K(d) values for the transmembrane domains of pPLN and PLN are approximately 60 microM), supporting the hypothesis that phosphorylation at Ser16 does not dissociate PLN from SERCA. However, the binding surface and dynamics in domain Ib (residues 22-31) change substantially upon phosphorylation. Since PLN can be singly or doubly phosphorylated at Ser16 and Thr17, we propose that these sites remotely control the conformation of domain Ib. These findings constitute a paradigm for how post-translational modifications such as phosphorylation in the cytoplasmic portion of membrane proteins control intramembrane protein-protein interactions.
 ...
PMID:Effects of Ser16 phosphorylation on the allosteric transitions of phospholamban/Ca(2+)-ATPase complex. 1656 56

We have used chemical synthesis, functional reconstitution, and electron paramagnetic resonance (EPR) to probe the functional dynamics of phospholamban (PLB), which regulates the Ca-ATPase (SERCA) in cardiac sarcoplasmic reticulum. The transmembrane domain of PLB inhibits SERCA at low [Ca(2+)], but the cytoplasmic domain relieves this inhibition upon Ser16 phosphorylation. Monomeric PLB was synthesized with Ala11 replaced by the 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) spin label, which reports peptide backbone dynamics directly. PLB was reconstituted into membranes in the presence or absence of SERCA. TOAC-PLB showed normal inhibitory function, which was reversed by phosphorylation at Ser16 or by micromolar [Ca(2+)]. EPR showed that the PLB cytoplasmic domain exhibits two resolved conformations, a tense T state that is ordered and a relaxed R state that is dynamically disordered and extended. PLB phosphorylation shifts this equilibrium toward the R state and makes it more dynamic (hyperextended). Phosphorylation strongly perturbs the dynamics of SERCA-bound PLB without dissociating the complex, while micromolar [Ca(2+)] has no effect on PLB dynamics. A lipid anchor synthetically attached to the N terminus of PLB permits Ca-dependent SERCA inhibition but prevents the phosphorylation-induced disordering and reversal of inhibition. We conclude that the relief of SERCA inhibition by PLB phosphorylation is due to an order-to-disorder transition in the cytoplasmic domain of PLB, which allows this domain to extend above the membrane surface and induce a structural change in the cytoplasmic domain of SERCA. This mechanism is distinct from the one that relieves PLB-dependent SERCA inhibition upon the addition of micromolar [Ca(2+)].
 ...
PMID:Phosphorylation-dependent conformational switch in spin-labeled phospholamban bound to SERCA. 1657 47