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

Neonatal lead exposure produces selective rod degeneration and functional deficits in adult hooded rats. Similar alterations occur following retinal exposure to ouabain. This study determined whether there were long-term effects of neonatal lead exposure on rat retinal or renal Na+,K(+)-ATPase (Na,K-ATPase) activity and employed in vitro studies to examine the mechanism of ionic lead (Pb2+)-induced inhibition of retinal Na,K-ATPase. Pups, exposed to lead only via the milk of dams consuming 0, 0.02, or 0.2% lead solutions, had mean blood lead concentrations of 1.2, 18.8, and 59.4 micrograms/dl at weaning, respectively, and 5-7 micrograms/dl as adults. Prior lead exposure produced significant dose-dependent decreases in isolated retinal Na,K-ATPase activity (-11%; -26%) whereas activity in the kidney was unchanged. In contrast, Na,K-ATPase from both isolated control tissues was inhibited by Pb2+. The half-maximal inhibitory dose (I50) of Pb2+ for retinal and renal Na,K-ATPase was 5.21 x 10(-7) and 1.25 x 10(-5) M, respectively. The Hill coefficient of the retina was 0.42 whereas it was 0.88 in the kidney. With MgATP as a substrate, the Pb(2+)-induced inhibition of retinal Na,K-ATPase was competitive and reversible with a Ki of 2.1 x 10(-7) M. Retinal and renal Na,K-ATPase were 20-fold and 1.1-fold more sensitive to inhibition by Pb2+ than by Ca2+, respectively. The Pb(2+)-induced inhibition of retinal Na,K-ATPase was antagonized by Na+, potentiated by Mg2+, not altered by K+ or Ca2+, and prevented by ATP. Kinetic and competition studies with the retinal Na,K-ATPase establish that the Pb(2+)-induced inhibition is complex. The increased sensitivity of retinal, compared to renal, Na,K-ATPase to inhibition following in vivo or in vitro lead exposure may relate to their different alpha subunit composition. This is speculated to play a fundamental role in the target organ toxicity of lead.
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PMID:Developmental lead exposure inhibits adult rat retinal, but not kidney, Na+,K(+)-ATPase. 164 99

The olfactory epithelium is comprised of bipolar sensory neurons, sustentacular cells, and basal cells. The sensory neurons have apical knobs and cilia, which project into the olfactory mucus toward the nasal lumen, and represent presumptive sites of odorant binding. Ionic currents, measured across this epithelium in both the resting and odorant-stimulated states, are known to be sustained, at least in part, by active transport of sodium. Information identifying the cellular sites of ion transport in olfactory sensory epithelium will therefore aid in elucidating the ionic mechanisms associated with olfactory transduction. The membrane-bound enzyme Na+/K(+)-ATPase mediates active ion transport in many other cells and tissues. We have consequently employed the cytochemical technique reported by Ernst (J. Histochem. Cytochem., 20 (1972) 23-38, 1322) to identify possible sites of elevated Na+/K(+)-ATPase activity in olfactory epithelium. This procedure detects inorganic phosphate (Pi) released from an artificial substrate (nitrophenyl phosphate) by enzyme catalytic activity. In the presence of strontium ion. Pi is precipitated near regions of high enzymatic activity, then converted to a product visible in the electron microscope. Parallel control preparations were incubated in media (1) supplemented with the specific Na+/K(+)-ATPase inhibitor ouabain (to abolish formation of specific reaction product); (2) with substrate deleted (to demonstrate possible non-specific binding of Sr2+ and/or Pb2+); or (3) with the necessary cofactor K+ deleted. In tissues incubated for demonstration of Na+/K(+)-ATPase activity, reaction product was associated with apical knobs, cilia and dendrites of olfactory receptor neurons at the apical surface. In the more proximal region of the epithelium, reaction product was associated with cell bodies and axons of the sensory neurons, and with the lateral membranes of sustentacular cells. Reaction product was deposited intracellularly, compatible with the known mechanism of the Na+/K(+)-ATPase enzymatic reaction. In control specimens incubated with ouabain, with substrate deleted, or with K+ deleted, only a small quantity of non-specific precipitate was observed. These results are discussed with reference to the various sodium currents implicated in olfactory transduction and transepithelial transport.
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PMID:Ultrastructural localization of Na+/K(+)-ATPase in rodent olfactory epithelium. 164 70

Lead (Pb) inhibited the activities of Na(+)-K+ ATPase (IC50 = 2.0 x 10(-6) M), K(+)-Para-Nitrophenyl phosphatase (PNPPase) (IC50 = 3.5 x 10(-6) M) and [3H]-ouabain binding (IC50 = 4.0 x 10(-5) M) in rat brain P2 fraction. A variable temperature or pH significantly elevated the inhibition of Na(+)-K+ ATPase by Pb in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation of Na(+)-K+ ATPase by ATP was indicated by a variation in Vmax values with no significant changes in Km values at any temperature studied. In the presence of Pb, for Na(+)-K+ ATPase at pH 6.5 and 8.5, Vmax was decreased with an increase in Km values suggesting a mixed type of inhibition. Sulfhydryl agents such as dithiothreitol (DTT) and cysteine (Cyst), but not glutathione (GSH) offered varied levels of protection against Pb-inhibition of Na(+)-K+ ATPase at pH 7.5 and 8.5. The present data suggest that inhibition of Na(+)-K+ ATPase by Pb is both temperature and pH-dependent. These results also indicate that Pb inhibited Na(+)-K+ ATPase by interfering with phosphorylation of enzyme molecule and dephosphorylation of the enzyme-phosphoryl complex and exerted an effect similar to that of SH-blocking agents.
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PMID:Effects of lead on pH and temperature-dependent substrate-activation kinetics of ATPase system and its protection by thiol compounds in rat brain. 166 9

The effect of Cd2+, Pb2+ and Hg2+ on the Ca(2+)-ATPase activity of sarcoplasmic reticulum from rabbit muscle was studied. The concentration of relevant free and complex species for the assay conditions have been computed. As a result, ATP hydrolysis was found to be inhibited with an IC50 value of 950 nmol/l free Cd2+ or 95 nmol/l free Pb2+. Although calculation of the free Hg2+ was not possible, the comparison of the IC50 values for total metal ions show that Hg2+ is the strongest inhibitor of enzyme activity. The inhibition by Cd2+ seems to be independent of substrate concentration, whereas the inhibitory effect of Pb2+ is lowered in the presence of higher MgATP concentrations. Our data illustrate that the three heavy metals are potent inhibitors of the Ca2+ pump. Therefore low concentrations of these metal ions may disturb intracellular Ca2+ homeostasis and act on Ca(2+)-mediated cell functions.
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PMID:Inhibition of sarcoplasmic reticulum Ca(2+)-ATPase activity by cadmium, lead and mercury. 184 35

Certain heavy metal actions such as Cd2+ and Pb2+ mimic Ca2+ effectively in stimulating calmodulin (CaM). We now show that these cations also activate skeletal muscle troponin C (TnC), a Ca2(+)-binding protein highly homologous to CaM. Like Ca2+, these cations allow TnC to alter its electrophoretic mobility on polyacrylamide gels, and to bind to phenyl-Sepharose. Moreover, they activate TnC to stimulate myofibrillar ATPase. When TnC was removed from the skeletal myofibrils by treatment with trans-1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid (CDTA), the ATPase activity was no longer stimulated by the cations. However, after reconstitution of CDTA-treated skeletal myofibril with TnC, the response of ATPase to Ca2+, Cd2+ or Pb2+ was restored. These findings suggest that the activation of myofibrillar ATPase by Cd2+ and Pb2+ is mediated through TnC. The ability of the heavy metals to stimulate TnC-supported ATPase activity correlated quite well with the ability to increase the extent of the myofibrillar superprecipitation. The activation of TnC by Cd2+ or Pb2+ could constitute a possible molecular basis for their toxicity.
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PMID:Activation of troponin C by Cd2+ and Pb2+. 214 67

Lead (Pb) inhibited K(+)-stimulated para-nitrophenyl phosphatase (K(+)-PNPPase) of rat brain P2 fraction in a concentration-dependent manner with IC50 3.5 microM. Altered pH versus activity demonstrated comparable inhibitions by Pb in buffered acidic, neutral and alkaline pH ranges. Inhibition of enzyme activity was higher at lower temperatures (17-27 degrees C) compared to 37 degrees C. Preincubation of enzyme with sulfhydryl (-SH) agents such as cysteine (Cyst) and dithiothreitol (DTT) but not glutathione (GSH) protected against Pb-inhibition. Uncompetitive type of inhibition with respect to the activation of K+ was indicated by a decrease in Vmax from 16.2 to 8.37 mumoles of para-nitrophenol (PNP)/mg protein/hr and Km from 18.99 to 12.39 mM. Kinetic studies on substrate (p-nitrophenyl phosphate) activation in the presence of Pb (3.5 microM) indicated a significant decrease in Vmax from 8.94 to 4.69 mumoles of PNP/mg protein/hr with no change in Km. Cyst (3 microM) and DTT (10 microM) reversed the Pb-inhibited Vmax from 4.69 to 8.38 and 7.24 mumoles of PNP/mg protein/hr respectively. These results suggest that the critical conformational property of K(+)-PNPPase is sensitive to Pb. The data also indicates that the Pb inhibits Na(+)-K+ ATPase system by interacting with dephosphorylation of the enzyme-phosphoryl complex, while Cyst and DTT protected against Pb-inhibition.
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PMID:Effects of lead on K(+)-para-nitrophenyl phosphatase activity and protection by thiol reagents. 216 61

The (Na+ + K+)-ATPase is localized to the cerebral endothelium, i.e. the blood-brain barrier, and is important for the maintenance of the brain electrolyte environment. Data from the present study indicate that Pb2+ inhibits the binding of [3H]ouabain to the cerebral microvascular (Na+ + K+)-ATPase in a time- and dose-dependent manner. Pb2(+)-induced inhibition developed slowly with a maximum obtained after 40 min. Inhibition of [3H]ouabain binding to the enzyme was 48% at 10 microM Pb2+ and appeared maximal (89%) at 100 microM Pb2+ when compared to [3H]ouabain binding in untreated microvessels at 40 min. In contrast, 100 microM Al3+ caused a 55% increase in [3H]ouabain binding to the (Na+ + K+)-ATPase, relative to untreated microvessels at 40 min. Insulin or bovine serum albumin stimulated [3H]ouabain binding to the enzyme when added at similar concentrations. However, the addition of both insulin and bovine serum albumin did not result in an additive effect. These results show that insulin exerts a nonspecific effect on [3H]ouabain binding to the (Na+ + K+)-ATPase similar to that evoked by bovine serum albumin. However, the metal ions Pb2+ and Al3+ provoke selective alterations in the cerebromicrovascular (Na+ + K+)-ATPase with Pb2+ inhibiting and Al3+ stimulating [3H]ouabain binding.
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PMID:Control of [3H]ouabain binding to cerebromicrovascular (Na+ + K+)-ATPase by metal ions and proteins. 216 70

1. Lead, ouabain and an endogenous plasma inhibitor were all found to be potent inhibitors of purified hog cerebral cortex sodium-potassium-activated adenosine triphosphatase and potassium-stimulated p-nitrophenyl-phosphatase. 2. The kinetic characteristics of inhibition of both enzymes by lead and the endogenous plasma inhibitor differed in several respects. For sodium-potassium-activated adenosine triphosphatase, lead and the endogenous plasma inhibitor were non-competitive inhibitors with respect to potassium; lead was competitive with respect to sodium, whereas the endogenous plasma inhibitor had no effect; lead was competitive with respect to magnesium adenosine triphosphate, whereas the endogenous plasma inhibitor was uncompetitive. For potassium-activated p-nitrophenylphosphatase, both lead and the endogenous plasma inhibitor were competitive with respect to potassium; lead showed a mixed type of inhibition with respect to p-nitrophenylphosphate, whereas the endogenous plasma inhibitor was non-competitive. 3. Lead and the endogenous plasma inhibitor exhibited synergistic inhibitory activity on sodium-potassium-activated adenosine triphosphatase. 4. These results suggest that lead could play a contributory role in the pathogenesis of essential hypertension via an additive inhibition of vascular smooth muscle sodium-potassium-activated adenosine triphosphatase.
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PMID:Effects of lead and a low-molecular-weight endogenous plasma inhibitor on the kinetics of sodium-potassium-activated adenosine triphosphatase and potassium-activated p-nitrophenylphosphatase. 216 8

A modified ATPase method for the simultaneous demonstration of capillaries and fiber types in skeletal muscle is presented. Muscle biopsies were obtained from mice, hamsters, rats, cats, and dogs, quick frozen, and sectioned at 8 microns in a cryostat. The frozen slides were fixed in a neutral formalin solution at 4 C for 5 min, and then incubated at 37 C for 1 hr in a medium containing ATP, Pb2+, and Ca2+ in a tris-maleate buffer (pH 7.2). Dilute (NH4)2S was used as a developer. To test the reliability of the proposed method, serial sections of each biopsy were stained separately for capillaries (amylase-PAS method) and for fiber types by a standard myosin ATPase (m-ATPase) method. Fiber type percent and capillary parameters were determined for each biopsy. No difference in results was observed for parameters determined using the modified ATPase method compared to the standard capillary and fiber type staining methods. This modified technique is therefore suitable for the simultaneous demonstration of capillaries and fiber types in skeletal muscle.
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PMID:A histochemical method for the simultaneous demonstration of capillaries and fiber type in skeletal muscle. 244 Jan 55

Intermolt adult crayfish P. clarkii were used for this work. After acclimatization to laboratory conditions crayfish were exposed to sublethal concentrations of cadmium, mercury, and lead for 96 h. Gills of control and exposed crayfish were removed and ATPase activity and oxygen uptake rate were determined. Structural damage of gill filaments was also observed. Gill tissue respiration rates were measured for individual crayfish using a Gilson differential respirometer. Lead causes a decrease of gill oxygen uptake, but neither cadmium nor mercury seems to affect it at the concentrations employed. Although all metals studied alter gill filament structure, lead damage is the most apparent. In the same way, significant differences in gill ATPase activity owing to metal exposure were only observed in lead treated crayfish.
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PMID:Cadmium, mercury, and lead effects on gill tissue of freshwater crayfish Procambarus clarkii (Girard). 248 11


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