Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.16.2 (PCP)
 3,761 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hypothesis that the ADP-sensitive form of phosphorylated Na+, K+-ATPase contains occluded sodium ions has been tested by a procedure which involves (i) modifying the enzyme with alpha-chymotrypsin or N-ethylmaleimide (NEM) so that the ADP-sensitive form is more stable than it is in the native enzyme, (ii) phosphorylating the modified enzyme with ATP in the presence of labelled sodium ions, and (iii) forcing the phosphorylated enzyme rapidly through a cation-exchange column and measuring the labelled sodium in the effluent. The results show that ADP-sensitive phosphoenzyme prepared from alpha-chymotrypsin- or NEM-modified Na+, K+-ATPase is able to carry labelled sodium ions through a cation-exchange resin. This behaviour was not seen with native Na+, K+-ATPase or when phosphorylation was prevented by the omission of magnesium ions or by the substitution of adenylyl(beta, gamma-methylene)diphosphonate (AMP-PCP) for ATP. The occluded sodium ions were rapidly released when the phosphoenzyme was dephosphorylated by ADP. When alpha-chymotrypsin-modified enzyme was phosphorylated by ATP with 1 mM-sodium in the medium, close to three sodium ions were occluded per phospho group. The stoicheiometry at much lower sodium concentrations could not be determined satisfactorily. A consideration of the rate constants of the reactions thought to be involved in the occlusion of sodium and in the release of sodium from the occluded state shows that, so far as they are known, these constants are compatible with the hypothesis that the occluded-sodium form of the phosphoenzyme plays a central role in sodium transport through the pump.
 ...
PMID:The occlusion of sodium ions within the mammalian sodium-potassium pump: its role in sodium transport. 608 5

Several pollutants like DDT, atrazine, PCP, and others induce changes of cortisol and glucose levels in serum, variations of the amount of liver glycogen and liver function, and exert changes of the activity of gill ATPase and acetylcholinesterase in brain and serum of carps. There is always a biphasic response, an increase of concentration or enzyme activity for a short time, and a decrease or inhibition of the enzymes after a longer exposure to the pollutants. The time scale, the duration of the period of increase and that of decrease, depends on the concentration and the toxicity of the pollutants. The influence of the pollutants in normal fresh water was compared with the effects occurring in carps acclimated to 1.2% salt water. This condition enables one to show that the carps are more sensitive to the pollutants under this condition. All responses are unspecific. Advice for the use of these tests as criteria for water quality are given.
 ...
PMID:Physiological changes in carps induced by pollution. 622 18

1. Changes in the intrinsic fluorescence of Na, K-ATPase protein have been used to monitor the interconversion of E(1) (low fluorescence) and E(2) (high fluorescence) forms of the unphosphorylated enzyme.2. In media lacking sodium and nucleotides, 1 mM-potassium was sufficient to convert practically all of the enzyme into the E(2) form. In media containing 1 mM-potassium, 1 mM-EDTA, and no sodium or magnesium, the addition of ATP, or its beta, gamma-imido or methylene analogues, converted the enzyme back into the E(1) form. The relation between nucleotide concentration and the fraction of the enzyme that was in the E(1) form could be described by a rectangular hyperbola, with a K((1/2)) of about 15 muM for ATP, 65 muM for adenylyl-imidodiphosphate (AMP-PNP) and 180 muM for adenylyl (beta, gamma-methylene)-diphosphonate (AMP-PCP). ADP also converted the enzyme back into the E(1) form, with a K((1/2)) of about 25 muM, but the relation between concentration and fraction converted was not well described by a rectangular hyperbola.3. In similar media containing 50 mM-potassium, much higher concentrations of ATP were required to convert the enzyme back into the E(1) form, and the conversion was probably incomplete.4. If we assume that ATP and potassium ions affect each other's binding solely by altering the equilibrium between E(1) and E(2) forms of the enzyme, we are able to conclude (i) that potassium ions bind to the E(1) form with a moderately low affinity, (ii) that, in the absence of nucleotides, the equilibrium between E(1)K and E(2)K is poised strongly in favour of E(2)K, (iii) that the binding of ATP to a low-affinity site alters the equilibrium constant for the interconversion of E(1)K and E(2)K by two to three orders of magnitude, so that, at saturating levels of ATP, the equilibrium is probably slightly in favour of E(1)K, and (iv) that in sodium-free, potassium-containing media, ATP will appear to bind to the enzyme more tightly than would be expected from the dissociation constant of the E(2)K. ATP complex.5. The pattern of the equilibrium constants for the various reactions between E(1), E(2), ATP and potassium is compatible with the hypothesis that the ATP-accelerated conversion of E(2)K into E(1)K, and the subsequent release of potassium ions from low-affinity inward-facing sites, are part of the normal sequence of events during potassium influx in physiological conditions.
 ...
PMID:The equilibrium between different conformations of the unphosphorylated sodium pump: effects of ATP and of potassium ions, and their relevance to potassium transport. 624 81

Evidence in this and other reports from this laboratory suggest that adrenergic nerves in rat heart ventricle slices incubated in a Na+-deprived (choline+) medium containing Ca++ (Ch+--Ca++), transport (by a cocaine-sensitive mechanism) 3H-norepinephrine outwardly from synaptic vesicles attached or fused to the plasma membrane. The 3H-amine secretion was not inhibited by probenecid, an anion transport inhibitor which may prevent exocytosis. The 3H-amine release was rapidly inhibited by exogenous nucleotides ATP, UTP, and GTP greater than ADP greater than AMP greater than the nucleoside adenosine. Magnesium++ tended to increase and reserpine to decrease the effect of ATP. Neither increasing the [Ca++] nor [Mg++] (to compete with Ca++ for ATP) decreased the effect of 3 mM ATP. After secretion began, lowering the Ca++ concentration by ommission, or by the inclusion of either a low concentration of EDTA or the Ca++-binding, but non-energy-conserving synthetic analogs of ATP: AMP--PCP and AMP--PNP, gradually lowered the rates of secretion. By comparison, the rapid effects of the energy-conserving nucleotides suggested that their effects were at least partially independent of chelation, and were energy dependent. ATP, unlike cocaine, did not inhibit the uptake of NE in a Krebs HCO3 medium. Inhibition of (Na+ + K+)-ATPase by ouabain neither inhibited the release by Ch+--Ca++, nor antagonizes the release inhibiting effect of ATP. Hence, ATP did not increase apparent retention of NE by stimulating the uptake of released NE. The ATP-inhibited secretion was not increased by theophylline.
 ...
PMID:The effect of exogenous adenosinetriphosphate on the choline-calcium stimulated release of 3H-norepinephrine in rat heart ventricle slices. 668 77

ATP and ADP stimulated the release of specific prostaglandin products from the perfused rabbit kidney heart. The two nucleotides produced the same qualitative profile of prostaglandin products. In kidney, prostaglandin E2 was the major product, whereas in heart 6-keto prostaglandin F1 alpha and prostaglandin E2 predominated. ATP was a slightly more potent than ADP. ATP administered into the perfused heart to kidney was rapidly hydrolyzed to ADP and AMP. The prostaglandin E2 generating activity of ATP was increased 6-10 fold when ATP was given together with AMP-PCP or AMP-PNP which competitively inhibit the activity of vascular ATPase. Thus, the rapid hydrolysis of ATP reduces its agonistic activity for prostaglandin release. ATP and ADP administered together at maximal stimulating doses produced an additive response for prostaglandin E2 release. These results and the results of tachyphylaxis experiments indicate that ATP and ADP interact independently with different types of purinergic receptors.
 ...
PMID:Evidence for different purinergic receptors for ATP and ADP in rabbit kidney and heart. 732 99

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.
 ...
PMID:The modulation of Ca2+ binding to sarcoplasmic reticulum ATPase by ATP analogues is pH-dependent. 759 71

1. This paper identifies and characterizes an ATP-dependent copper transport system in endoplasmic reticulum vesicles isolated from male rat liver. 2. The transporter has a Km of 2.5 +/- 1.2 mumol 1(-1) copper glutathione (CuGSH) and a Vmax of 4.5 +/- 1.3 nmol (mg protein)-1 (5 min)-1 for copper. 3. At a copper concentration of 2 mumol l-1, ATP dependence reaches saturation, with a Km for ATP of 4.7 +/- 2.4 mmol l-1 and a Vmax of 2.8 +/- 0.6 nmol (mg protein)-1 (5 min)-1. 4. The uptake is dependent on ATP hydrolysis, since a low energy analogue of ATP, adenosine 5'-[beta-gamma-methylene] triphosphate tetralithium (AMP.PCP), has no effect on copper uptake. 5. The transporter is a P-type ATPase, since vanadate inhibits uptake with a high degree of specificity (100 mumol l-1 inhibits uptake by 50% at a copper concentration of 2 mumol l-1).
 ...
PMID:Identification of an ATP-dependent copper transport system in endoplasmic reticulum vesicles isolated from rat liver. 773 49

The structure of Ca(2+)-ATPase has been studied by electron microscopy of two different crystal forms: one tubular form induced by vanadate in native sarcoplasmic reticulum (SR) membranes and another multilamellar form grown from detergent-solubilized SR. To determine the conformation of Ca(2+)-ATPase within each crystal form, the respective effects of Ca2+, thapsigargin, adenosine 5'-(beta, gamma-methylene)triphosphate) (AMP-PCP), and chromium(III) (Cr-ATP) on crystallization have been studied. Vanadate-induced tubes were prevented from forming by micromolar Ca2+, but if preformed in the absence of Ca2_, millimolar Ca2+ was required to disrupt these crystals. Thapsigargin promoted tube formation even in the presence of 10 mM Ca2+. Neither AMP-PCP nor Cr-ATP prevented tube formation, and the Ca2+ sensitivity of tube formation from Cr-ATP-inhibited SR was identical to controls. Multilamellar crystals required at least 0.2 mM Ca2+ and were prevented from forming by thapsigargin, AMP-PCP, or Cr-ATP. It is concluded that helical tubes are composed of the Ca(2+)-free, dephosphorylated conformation (E), and the nucleotide-bound conformation (E-ATP) is also tolerated. In contrast, multilamellar crystals are composed of the Ca(2+)-bound conformation (E.Ca2) and do not tolerate nucleotide binding. Thus, comparison of structures obtained from the two crystal forms should reveal physiologically relevant conformational differences.
 ...
PMID:Conformation of Ca(2+)-ATPase in two crystal forms. Effects of Ca2+, thapsigargin, adenosine 5'-(beta, gamma-methylene)triphosphate), and chromium(III)-ATP on crystallization. 815 94

Reticulomyxa transports particulates, like bacterial and algal prey items, bidirectionally along the outside of its pseudopodia. This cell surface transport and intracellular organelle transport can be reactivated in detergent permeabilized cell models [Orokos et al., 1997: Cell Motil. Cytoskeleton]. We have used this unique system to compare cell surface and organelle mechanochemistry in situ in the same reactivated pseudopodia. The ATPase activities of both types of transport were indistinguishable; each displayed identical nucleoside triphosphate specificity, transport ATPase kinetics, and inhibitor sensitivity. Organelle and cell surface transport reactivation required "hydrolyzable" adenosine nucleoside triphosphates; neither reactivated with GTP, CTP, UTP, ITP, AMP-PNP, AMP-PCP, or ATP-gamma-S. However, other ATP analogues, such as 2'-deoxy-ATP and 3'-deoxy-ATP and 2',3'-dideoxy-ATP, supported the reactivation of organelle and cell surface transport at similar, but markedly reduced, velocities. Both transport processes were inhibited similarly by known inhibitors of dynein ATPases such as erythro-9-(3-[2-hydroxynonyl]) adenine (EHNA) or sodium (Na)-orthovanadate. N-ethylmaleimide (NEM) and ultraviolet (UV) irradiation in the presence of Na-orthovanadate and ATP permanently disabled both transport processes. Organelle and surface transport followed identical Michaelis-Menten kinetics with a calculated Km of 118 microM ATP and a maximum translocation velocity (Vmax) of 8.33 microm/sec. These findings strongly suggest that cell surface transport shares the same cytoplasmic dynein motor [Schliwa et al., 1991: J. Cell Biol. 112:1199-1203] that drives organelle transport.
 ...
PMID:Cell surface and organelle transport share the same enzymatic properties in Reticulomyxa. 938 17

Phencyclidine hydrochloride (PCP) also known as Angel Dust is a very potent psychotomimetic drug of abuse. Besides its central nervous system (CNS) effects PCP produces a number of adverse effects in a variety of tissues including the cardiovascular system. Since PCP is known to alter the cellular calcium homeostasis the present studies were initiated to determine the changes in cardiac Ca2+ ATPase activity in rats treated with PCP. For in vitro studies the cardiac sarcoplasmic reticulum (SR) fractions prepared from normal rats were incubated with 25, 50 and 100 microM PCP and the enzyme activities were estimated. Whereas, for in vivo studies the cardiac SR fractions prepared from rats treated with PCP (10 mg/kg body wt. single dose, intra-peritoneally (i.p.)) and sacrificed at different time intervals were used. PCP reduced the Ca2+ ATPase activity significantly both in vitro and in vivo. A 50% inhibition of the enzyme activity was obtained with 100 microM PCP in vitro. A significant reduction of SR Ca2+ ATPase was also evident as early as 1 h after treatment of rats with PCP. The reduction of Ca2+ ATPase activity in SR was irreversible even at 12 h after treatment. The in vitro kinetic studies revealed that PCP was found to be a competitive inhibitor of Ca2+ ATPase with respect to the substrate, ATP, and non-competitive with respect to Ca2+ activation. These results indicate that PCP alters the myocardial Ca2+ homeostasis by inhibiting the Ca2+ ATPase in cardiac SR in rats. Inhibition of SR Ca2+ ATPase may result in the impairment of contraction and relaxation coupling processes in the myocardium.
 ...
PMID:Phencyclidine block of Ca2+ ATPase in rat heart sarcoplasmic reticulum. 977 88


<< Previous 1 2 3 4 Next >>