Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To test the possibility that ATP diffusion limits the kinetics of myosin ATPase (EC. 3.6.1.3) in situ, myosin was covalently bound to the surface of 2 kinds of films: collagen and Immunodyne. On collagen films, it was bound either with 1-ethyl-3 (3 dimethyl-aminopropyl)carbodiimide (EDC) or with dimethyl-3,3'-dithiobis(propionimidate) (DTP). The apparent Km for K+-ATP rose from 0.26 mM for free myosin in solution to 2-5 mM for covalently bound myosin, and maximum K+-ATPase activity was very low. With the other film, Immunodyne from Pall, the maximum activity of bound myosin was 170 nmol per min per 1.5 cm2 film. The apparent Km for K+-ATP was 2.1 mM when the incubation mixture was vigorously stirred, and the effect of stirring indicated that the kinetics of K+-ATP hydrolysis are limited by external diffusion. The large amount of myosin bound per unit of Immunodyne film surface permitted the study of Mg2+-ATPase activity, although it was 400-500 times less than the K+-ATPase activity. The apparently non-Michaelian kinetics of Mg2+-ATP hydrolysis are attributable to the external diffusion. The apparent Michaelis constant observed at low Mg2+-ATP concentrations rose from 0.27 microM for myosin in solution to 5 microM for myosin bound to Immunodyne film.
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PMID:Diffusion-limited kinetics of immobilized myosin ATPase. 252 82

Male adult Wistar rats were treated for 8 weeks with an organosilicone [2,2-dimethyl-4-(chloromethyl)-1,3-dioxa-2-silacyclopentane] employing two different dosages (25 and 50 mg/kg body weight i.p. daily) and the changes in the tubular apparatus of the kidney were investigated employing histological and enzyme-histochemical methods. The effects, more pronounced at the higher dosage, were the following: The brush borders of the proximal tubules were stuck together and disintegrated; only few epithelial cells remained intact showing a decreased activity of nonspecific esterases and the increase of beta-hydroxybutyric acid dehydrogenase. The nuclei of most of the epithelial cells in the distal tubules were dislocated towards the enlarged lumen and the cytoplasma showed a decrease of nonspecific esterases and an increase of beta-hydroxybutyric acid dehydrogenase. The collagen fibers in the walls of the collecting tubules were dislocated and disintegrated with a discontinuous border of Mg2+-ATPase; the nuclei of the epithelial cells were pyknotic, the cytoplasma showed an increase of beta-hydroxybutyric acid dehydrogenase. The induced changes were partially reversible after a recovery period of 8 weeks.
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PMID:Effects of an organosilicon compound on the tubular apparatus of rat kidney. A histological and enzyme histochemical report. 296 64

The asymmetric distribution of phospholipids in the plasma/organellar membranes is generated and maintained through phospholipid flippases in resting cells, but becomes disrupted in apoptotic cells and activated platelets, resulting in phosphatidylserine (PS) exposure on the cell surface. Stable PS exposure during apoptosis requires inactivation of flippases to prevent PS from being reinternalized. Here we show that flippase ATP8A1 is highly expressed in both murine and human platelets, but is not present in the plasma membrane. ATP8A1 is cleaved by the cysteine protease calpain during apoptosis, and the cleavage is prevented indirectly by caspase inhibition, involving blockage of calcium influx into platelets and subsequent calpain activation. In contrast, in platelets activated with thrombin and collagen and exposing PS, ATP8A1 remains intact. These data reveal a novel mechanism of flippase cleavage and suggest that flippase activity in intracellular membranes differs between platelets undergoing apoptosis and activation.
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PMID:Calpain cleaves phospholipid flippase ATP8A1 during apoptosis in platelets. 3067 56