Inhibition of Na+,K(+)-ATPase by flavonoids and their inotropic effect. Investigation of the structure-activity relationship.

The relationship between the structures of 39 natural flavonoids (including flavones, flavonols, flavonones, and isoflavones) and their inhibitory and positive inotropic effects have been found. It is shown that flavonoids considerably inhibit the activity of the purified preparation of pig kidney medulla Na+,K(+)-ATPase with Ki = 1.4-22.

[Interaction of spin labels and probes with Na+,K+-ATPase].

Localization of the PCMB-R spin label and benzocarboline probe bound with the purified preparation of pig kidney-Na+, K(+)-ATPase relative to active site of the enzyme was studied by EPR method. The number of Mn2+ ions in active site of the enzyme as well as that bound with lipids was determined from EPR spectra of paramagnetic manganese ions replacing magnesium ions were measured in frozen protein samples of Na2+, K(+)-ATPase at 77 K. It has been found that sulfhydryl group of the enzyme modified by PCMB-R and benzocarboline probe are placed at distances 38 A and 50 A, respectively, from Mn2+ ions in the active site of Na+, K(+)-ATPase.

[The use of triplet-sensitized photochromism phenomenon for the study of dynamic interaction of membrane proteins].

Possibility of registration of protein interactions in the membranes was demonstrated. The membrane preparation of Na+, K+ ATPase was used in the investigations. The Na+, K+ ATPase was bound with 4-acetoamido-4'-isothiocyanatostilbene-2,2' disullfonic acid (SITS) and erythrosinisothiocyanate (ERITC).

[Effect of transformed steroids on Na,K-dependent ATPase].

The transformed steroids containing delta 5-3 beta-hydroxy- or 3 beta, 5 alpha-dihydroxy-6-keto groups in the A/B rings and an additional cycle E (17,20-dihydroxy-delta-lactone, 16,23-pyranone or delta 20(22)-16 alpha, 17 alpha-dihydroxy-23-carbethoxy-side chain) (1 . 10(-5) M) inhibit Na+,K+-ATPase from pig kidney medulla or from ox brain. The steroid structure has a noticeable effect on ATPase inhibition varying from 3 to 26%.