Inhibition of mitochondrial F₁ ATPase and sarcoplasmic reticulum ATPase by hydrophobic molecules

Abstract

The hydrophobic nature of the active site of two energy-transducing ATPases was explored by comparing interactions between Pi and each of three hydrophobic drugs in the absence and presence of organic solvents. The drugs tested were the Fe . bathophenanthroline complex and the anticalmodulin drugs, calmidazolium and trifluoperazine. All inhibit the Pi in equilibrium with ATP exchange reaction catalyzed by submitochondrial particles and the ATPase activity of both submitochondrial particles and soluble F1 ATPase. The inhibition by the three drugs is reversed by either raising the Pi concentration or by adding organic solvent (dimethylsulfoxide, ethyleneglycol or methanol) to the medium. The inhibition of the Pi in equilibrium with ATP exchange by trifluoperazine becomes more pronounced when the electrochemical proton gradient formed across the membrane of the submitochondrial particles is decreased by the addition to the medium of the proton ionophore carbonylcyanide p-trifluoromethoxyphenylhydrazone. The ATPase activity and the Ca2+ uptake by sarcoplasmic reticulum vesicles are inhibited by the Fe . bathophenanthroline complex, calmidazolium and trifluoperazine. Phosphorylation of the ATPases by Pi, synthesis of ATP from ADP and Pi and the fast efflux of Ca2+ observed during reversal of the Ca2+ pump are inhibited by the three drugs. The inhibition is reversed by raising the concentration of Pi or dimethylsulfoxide. The three drugs tested appear to compete with Pi for a common binding site on the Ca2+-ATPase. The data presented are interpreted according to the proposal that the catalytic site of an enzyme involved in energy transduction undergoes a hydrophobic-hydrophilic transition during the catalytic cycle.

In vitro photosensitization of tumour cell enzymes by Photofrin II administered in vivo

“…Also, it has been proposed that the haems and coppers may be bound to subunits I and II, although subunits V and VII have also been implicated as haem binding sites (Azzi, 1980). Likewise it appears that the active site of mitochondrial F, ATPase, and of the Ca2 +-ATPase of the sarcoplasmic reticulum, is hydrophobic in nature, since both enzymes were inhibited by hydrophobic drugs, an effect reversed by the presence of organic solvents (DeMeis et al, 1988 (Singh et al, 1987;Moreno et al, 1987), HpD (Berns et al, 1982) and haematoporphyrin (Salet et al, 1983). The data obtained here demonstrate the existence of a drug-dose related response of mitochondrial photosensitisation to Photofrin II.…”

“…Under the conditions studied here, the order of photosensitivity was cytochrome c oxidase > FOF ATPase > succinate dehydrogenase > NADH dehydrogenase. Cytochrome c oxidase, however, may possess some intrinsic properties that render it more sensitive to damage induced by porphyrin photosensitisation, such as the presence of hydrophobic regions where porphyrins may accumulate, since subunits I, II, III and VII display binding of hydrophobic reagent probes (DeMeis et al, 1988). Also, it has been proposed that the haems and coppers may be bound to subunits I and II, although subunits V and VII have also been implicated as haem binding sites (Azzi, 1980).…”

The Ca2+-ATPase Isoforms of Platelets Are Located in Distinct Functional Ca2+ Pools and Are Uncoupled by a Mechanism Different from That of Skeletal Muscle Ca2+-ATPase

“…In addition to increasing passive Ca 2ϩ efflux, trifluoperazine inhibits Ca 2ϩ uptake and ATPase activity in sarcoplasmic reticulum vesicles (13)(14)(15)(16)44). These effects were also observed with platelet vesicles, where trifluoperazine inhibited both Ca 2ϩ uptake and ATPase activity in lower concentrations than those necessary for sarcoplasmic reticulum vesicles (Fig.…”

“…This was first observed with arsenate, a phosphate analog that interacts with the catalytic site of the Ca 2ϩ ATPase, increasing the rate of Ca 2ϩ efflux and inhibiting the synthesis of ATP (10 -12). Similar to arsenate but in concentrations two orders of magnitude lower, a wide variety of hydrophobic drugs such as phenothiazines (13)(14)(15)(16), local anesthetics (17), and fatty acids (18) can also uncouple the Ca 2ϩ pump, greatly increasing the efflux of Ca 2ϩ from the vesicles. Ligands and substrates of the ATPase block the Ca 2ϩ efflux through the Ca 2ϩ pump promoted both by arsenate and hydrophobic drugs (11,13,14,16).…”

Prolyl Endopeptidase Inhibitors from the Underground Part of Rhodiola sachalinensis

“…Previously, this compound was reported as a synthetic lipid activator, although the spectral data could not be compared because the data were not reported in the literature. 17) Thus, this is the first report of the isolation from a natural source.…”