Effects of quercetin and F1 inhibitor on mitochondrial ATPase and energy-linked reactions in submitochondrial particles

Effects of inhibitors on the plasma membrane and mitochondrial adenosine triphosphatases of Neurospora crassa

A comparative study has been made of the effects of a variety of inhibitors on the plasma membrane ATPase and mitochondrial ATPase of Neurospora crassa. The most specific inhibitors proved to be vanadate and diethylstilbestrol for the plasma membrane ATPase and azide, oligomycin, venturicidin, and leucinostatin for mitochondrial ATPase. N,N'-Dicyclohexylcarbodiimide, octylguanidine, triphenylsulfonium chloride, and quercetin and related bioflavonoids inhibited both enzymes, although with different concentration dependences. Other compounds that were tested (phaseolin, fusicoccin, deoxycorticosterone, alachlor, salicyclic acid, N-1-napthylphthalamate, triiodobenzoic acid, cyclic AMP, cyclic GMP, theobromine, theophylline, and histamine) had no significant effect on either enzyme. Overall, the results indicate that the plasma membrane and mitochondrial ATPases are distinct enzymes, in spite of the fact that they may play related roles in H+ transport across their respective membranes.

Flavonoid compounds are potent inhibitors of cyclic AMP phosphodiesterase

The inhibitory activity of 19 flavonoid molecules on cyclic AMP breakdown by a commercial beef heart phosphodiesterase preparation is reported. 7 compounds are active in the micromolar range, 2 of which have a potency equivalent to that of papaverine. Some structure activity relationships are drawn.

Solubilization and some properties of the Mg2+-activated adenosine triphosphatase from Trypanosoma cruzi

1. Grinding of epimastigotes of Trypanosoma cruzi with glass powder in a mortar yielded a Mg2+-activated adenosine triphosphatase (ATPase) preparation which was highly sensitive to oligomycin. 2. Chloroform treatment of the particles resulted in the solubilization of an ATPase which was (a) activated by MgCl2; (b) slightly inhibited by CaCl2; (c) activated by sulphite and bisulphite; (d) had an optimum pH of 7.6; and (e) had a Km for ATP of 2.1 mM (in the presence of 4 mM MgCl2). 3. The solubilized enzyme was insensitive to oligomycin and leucinostatin, which inhibited the membrane-bound ATPase, though inhibited by efrapeptin and quercetin. 4. The results indicate that the chloroform-extracted enzyme is a soluble F1-ATPase similar to those isolated from mammalian mitochondria.

Bacillus megaterium mutant deficient in membrane-bound adenosine triphosphatase activity

An adenosine triphosphatase (ATPase) mutant of Bacillus megaterium was isolated and characterized. This mutant (designated A37) was unable to grow on nonfermentable carbon sources and possessed less than 5% of the wild-type ATPase activity. Oxygen uptake by the mutant was comparable to that in the wild type. Sporulation in the wild type occurred in both glucose- and nitrogen-limiting media; however, A37 sporulated only in the nitrogen-limiting medium. The inability of A37 to sporulate in glucose-limiting medium seemed to be due to insufficient adenosine 5'-triphosphate (ATP) levels during the sporulation stages. Fructose, which can generate ATP via substrate-level phosphorylation, is equally efficient in stimulating ATP synthesis in the wild type and A37. Malate-stimulated ATP synthesis in the wild type was shown to have many characteristics associated with oxidative phosphorylation and was absent in the mutant. These data suggest that the ATPase deficiency results in the loss of oxidative phosphorylation.

Bioflavonoid regulation of ATPase and hexokinase activity in Ehrlich ascites cell mitochondria

(1) The mitochondrial ATPase (EC 3.6.1.3) Ehrlich ascites cell mitochondria, was inhibited by D-glucose under physiological concentrations of ATP. The generation of ADP by the mitochondrial bound hexokinase, seems to be the reason for the D-glucose inhibitory effect. Reversal of the inhibitory effect of ADP on Ehrlich ascites cell mitochondria ATPase by an ATP-regenerating system was achieved. (2) Dissociation of mitochondrial bound hexokinase from the mitochondria eliminated the inhibitory effect of D-glucose. Rebinding of the hexokinase to the mitochondria regenerated the D-glucose inhibitory effect on Ehrlich ascites cell mitochondria ATPase. (3) Bioflavonoids such as quercetin inhibit the mitochondrial hexokinase activity, but do not change the mitochondrial ATPase activity of isolated Ehrlich ascites tumor cell mitochondria. (4) The inhibitory effect of bioflavonoids on mitochondrial bound hexokinase activity is shown to be dissociable from the ascites tumor cell mitochondria and seems to be associated with regulatory rather than catalitic sites of the enzyme.

Why do tumor cells have a high aerobic glycolysis?

In Ehrlich ascites cells and several other tumors, the high aerobic glycolysis is maintained by generation of ADP and Pi by the plasma membrane Na+K+ ATPase. The high ATP activity is caused by a defective pump that operates at a low efficiency. Studies of the mechanism of action of the Na+K+ ATPase and other pump ATPases suggest several alternative mechanisms that might account for the decreased efficiency. The possibility of involvement of a proteolipid is under investigation.

Influence of the flavonoid (+)-catechin on the permeability of Ehrlich mouse ascites tumour cell membranes

The effect of the flavonoid (+)-catechin and its hydrophilic derivative epicatechinsulphonate on the permeability of Ehrlich mouse ascites tumour cells (EMAT) was investigated. As a sensitive assay, the transmembrane fluxes of two different solutes were measured, the inwardly directed free diffusion of 14C-thiourea, and the carrier-mediated efflux of intracellularly accumulated 12C-1-aminocyclopentane-1-carboxylic acid. (+)-Catechn was found to reduce the permeability of EMAT membranes for both solutes. The primary target of the drug appears to be the membrane itself. The effectiveness of the drug was dependent on its concentration. Inhibition of fluxes was observed at 0.86 mM; the inhibition gradually increased as the concentration was increased. In contrast to (+)-catechin, epicatechinsulphonate was rather ineffective, even at a concentration as large as 10 mM. The effect of (+)-catechin was seen within a few minutes after its addition. However, it was considerably intensified as the incubation was prolonged. The effectivity of (+)-catechin decreased with increasing cell density. Thus, the drug appears to be absorbed by the cells. From the various data and the observation that incorporation of a strong lipophobic sulphonate residue into the moderately lipophilic catechin molecule markedly lowers the effectivity of the flavonoid, it is concluded that (+)-catechin, as a membrane stabilizing drug, interacts directly with certain constituents of the cell envelope, presumably membrane lipids.

Pig heart mitochondrial ATPase : properties of purified and membrane-bound enzyme. Effects of flavonoids

Soluble ATPase (F1) has been purified from pig heart mitochondria. The purified enzyme had a high specific activity and was homogeneous as checked by ultracentrifugation and electrofocusing. It could be dissociated into subunits by cold-treatment or sodium dodecyl sulfate denaturation. The molecular weights of the two major and three minor subunits could be estimated by sodium dodecyl sulfate gel electrophoresis. The native enzyme had an isoelectric point of 5.2 while the cold-denatured enzyme showed three main bands focusing at pH 5.0, 5.2, and 5.4. Kinetic properties (Vm and Km (atp) have been compared for the soluble and membrane bound ATPase in presence of various anions. Inhibitory effects of Quercetin and other flavonoids have been tested in order to get an insight on the interaction between ATPase and its natural inhibitor.