Inhibition ofE. coli ATPase activity by a troponin component,TN-I,and by mitochondrial ATPase inhibitor

Summary The enzymic activity of Mg²⁺-or Ca²⁺-stimulated ATPase fromEscherichia coli was inhibited by one of the troponin components, TN-I, and by mitochondrial ATPase inhibitor (F₁-inhibitor). The inhibitory ability of component TN-I against Mg²⁺-stimulated ATPase activity was lost after digestion of component TN-I with trypsin. The Mg²⁺-stimulated ATPase activity inhibited by component TN-I was completely restored by the addition of another troponin component, TN-C.     

Effect of heat treatment on the ATPase activity of various sarcoplasmic reticulum preparations.

Ca2+-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45 degrees C, but for temperatures higher than 48 degrees C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present during heat treatment.     

Postnatal decline of (Ca2+ + Mg2+)-activated membrane ATPase in cattle red cells.

Acitivity of membrane bound (Ca2+ + Mg2+)-stimulated ATPase, associated with Ca2+ outward transport, in calf red cells is high at birth and declines with a rate constant of 0.041 d-1 after the 3rd week. The decline parallels the disappearance of fetal hemoglobin.     

Mg2+-HCO 3 − -ATPase and carbonic anhydrase in rat intestinal mucosa

Cellular and Molecular Life Sciences - Mg2+-dependent and HCO 3 − -stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the...     

Mg2+-HCO-3-ATPase and carbonic anhydrase in rat intestinal mucosa

Mg2+-dependent and HCO-3-stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the other gastrointestinal mucosa. This ATPase may be useful to neutralize the gastric acid in the duodenal lumen. Carbonic anhydrase seems to accomplish a subsidiary role in the above reaction.     

Effects of various inhibitors and 2,4-dinitrophenol on adenosine triphosphatase from Malpighian tubules ofLocusta migratoria L

Summary Both Mg²⁺-ATPase and HCO ₃ ^– -stimulated ATPase activity were inhibited by sodium azide and to a lesser extent ethacrynic acid and amiloride. 1 mM DNP stimulated Mg²⁺-ATPase activity by 22% and HCO ₃ ^– -stimulated ATPase activity by 7%.     

Inhibition of erythrocyte ATPase activity by aclacinomycin and reverse effects of ascorbate on ATPase activity

We studied the effect of aclacinomycin on human erythrocyte membrane enzymes. Aclacinomycin inhibited ATPase, including Na-K-dependent ATPase, ouabain insensitive ATPase and Ca-ATPase. However acetylcholinesterase was not inhibited by aclacinomycin. The ATPase activities were not inhibited by aclacinomycin if ascorbate was added to the incubation mixture. However other reducing agents, alpha-tocopherol, superoxide dismutase and catalase had no effect on ATPase activity. Ascorbate may protect membrane proteins and lipids from peroxidate damage.     

Effect of heat treatment on the ATPase activity of various sarcoplasmic reticulum preparations

Summary Ca²⁺-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45°C, but for temperatures higher than 48°C pronounced denaturation is observed. Heat denaturation is decreased if Mg²⁺ or K⁺ are present during heat treatment.Acknowledgments. This work was supported by research grants from Instituto de Alta Cultura (Grant No. CB/2) and the Calouste Gulbenkian Foundation. We are grateful to Drs.A. P. Carvalho andV. M. C. Madeira for many discussions and suggestions during the course of this work.     

The (Na+ + K+)-ATPase activity in brain of Quaking mice.

The (Na+ 4 K+)- and Mg2+-dependent ATPase distribution in several brain areas has been investigated in Quaking mutant mice characterized by myelin deficiency. A marked decrease of (Na+ + K+)-ATPase activity has been found in limbic structures, hypothalamus and cerebellum. The Mg2+-dependent activity did not change. A possible involvement of the impairment of the (Na+ + K+)-ATPase activity in the seizure susceptibility of this mice is discussed.     

A Ca2+-sensitive myosin light chain kinase, regulating pig carotid smooth muscle actomyosin ATPase

In this paper the correlation between phosphate incorporation into the regulatory light chain of myosin by a Ca2+-dependent myosin light chain kinase, and the Ca2+-sensitive ATPase activity and superprecipitation behaviour of arterial actomyosin, is described.     

Temperature acclimation of Mg2+Ca2+-myofibrillar ATPase from a cold-selective teleost, Salvelinus fontinalis: a compromise solution

Brook trout (Salvelinus fontinalis, Mitchill) were acclimated over 15 weeks to either +4 degrees C or +24 degrees C. The effects of temperature on myofibrillar Mg2+Ca2+-ATPase activities were investigated. In contrast to goldfish, temperature acclimation does not alter the kinetic properties of the brook trout myofibrillar ATPase. Activation energy (delta G not equal to) is lower and substrate turnover number is higher than values previously reported for cold-adapted stenotherms. Properties of brook trout ATPase appear to be a compromise enabling function across a broad temperature range. The different strategies of adapting to seasonal temperature variations are briefly discussed.     

ATPase activity in mercury intoxicated eels

Summary Eels intoxicated by lethal doses of HgCl₂ accumulate mercury in their gills. Mercury inhibits the ouabainsensitive Na+K+ATPase activity of gills involving the rupture of the fish NaCl balance.The author wishes to express his sincere gratitude to Professor A. Disteche and Professor E. Schoffeniels for discussions during the investigation. This research was carried out in participation in the Belgian National Research and Development Program on the Environment-Water-Sea Project-Office of the Prime Minister-Interministerial Commission for Science Policy and Programmation.     

A Ca2+-sensitive myosin light chain kinase,regulating pig carotid smooth muscle actomyosin ATPase1

Summary In this paper the correlation between phosphate incorporation into the regulatory light chain of myosin by a Ca²⁺-dependent myosin light chain kinase, and the Ca²⁺-sensitive ATPase activity and superprecipitation behaviour of arterial actomyosin, is described.Acknowledgment. The financial support of the Deutsche Forschungsgemeinschaft (SFB 90) is gratefully acknowledged.     

The role of distinct membrane components of the enzyme in the ouabain sensitivity of Na+/K+ ATPase]

Purified plasma membranes from a cell line derived from the murine plasmocytoma MOPC 173 exhibited a 50% inhibition of the Na+K+ ATPase by 120 muM ouabain. EDTA treatment of such membranes induced a drop in the ouabain concentration needed for 50% inhibition to 0.4 muM. Supernatants obtained after EDTA treatment were able to complement with Ca(++) + Mg++ the washed EDTA treated membranes which recover their original resistance.     

Role of tropomyosin in the sensitivity of (Na+ + K+) ATPase to ouabain]

EDTA treatment of isolated plasma membranes from MF2S cells increased 1,000 fold the sensitivity of (Na+ + K+) ATPase activity to ouabain. The original sensitivity of the enzyme to the drug is recovered after addition of tropomyosin together with Ca++ ions to the treated membranes.     

Inhibition of sarcolemmal Na, K, Mg ATPase from the guinea pig heart is not compatible with a homogeneous population of non-interacting ouabain receptors

The inhibition of sarcolemmal Na, K, Mg ATPase from the guinea pig heart by ouabain was evaluated with a coupled enzyme assay. Models of negative cooperativity and of two independent receptors fitted the inhibition data equally well. The analysis was not compatible with a homogeneous population of non-interacting ouabain receptors.     

Synaptosomal adenosine triphosphatase (ATPase) inhibition by organophosphates.

Chicken spinal cord adenosine triphosphatases (both Na+, K+ stimulated and ouabain insensitive) were inhibited by tri-o-tolyl phosphate (TOTP, a neurotoxic organophosphate which is not a cholinesterase inhibitor) and mevinphos (a non-neurotoxic compound but inhibitor of cholinesterases). The inhibition was concentration and time dependent, with an initial rapid drop in activity followed by a gradual exponential decline.     

Inhibition of sarcolemmal Na,K, Mg ATPase from the guinea pig heart is not compatible with a homogeneous population of non-interacting ouabain receptors

Summary The inhibition of sarcolemmal Na, K, Mg ATPase from the guinea pig heart by ouabain was evaluated with a coupled enzyme assay. Models of negative cooperativity and of two independent receptors fitted the inhibition data equally well. The analysis was not compatible with a homogeneous population of non-interacting ouabain receptors.Acknowledgments. The technical assistance of P. Mayr and G. Ruhland is gratefully acknowledged.     

Ornithine decarboxylase, S-adenosyl-L-methionine decarboxylase and arginine decarboxylase from Mycobacterium bovis (BCG)

Ornithine decarboxylase (ODC), S-adenosyl-L-methionine decarboxylase (AMDC) and arginine decarboxylase (ADC) activities were detected for the first time in extracts of Mycobacterium bovis (BCG). All the decarboxylases differed from corresponding known bacterial decarboxylases in that: a) ODC did not require GTP for activity; b) ODC was not inhibited by any known inhibitor of bacterial ODCs; c) AMDC and ADC did not require Mg2+-ion for activity and were not markedly inhibited by any known inhibitor of the decarboxylases of other bacteria.     

(Ca−Mg) ATPase activity of human erythrocyte membranes: Influence of incubation buffer

Summary Activity of the (Ca–Mg) ATPase of human red blood cell membranes is highly dependent on the specific buffer used in the ATPase assay. Activity is highest in histidine and/or imidazole buffers and is lowest in HEPES buffer.This research was supported by Public Health Service Grants AH-16436 and GM 00109-16. We wish to acknowledge the useful suggestions of Thomas R. Hinds and the excellent clerical assistance of Ms Laurie Asher.