Characterization of the macrocyclic carbon suboxide factors as potent Na,K-ATPase and SR Ca-ATPase inhibitors

Abstract

Recently discovered macrocyclic carbon suboxide (MCS) factors with the general formula (C 3 O 2) n were found to strongly inhibit rabbit and rat Na,K-ATPase as well as SR Ca-ATPase. Highly active MCS factors were obtained by a base/acid treatment of their lipophilic precursor isolated from plants. In the ESI-MS spectra, the dominant molar mass ion of 431 Da corresponds to a 1:1 complex of the carbon suboxide hexamer (n = 6; M r = 408 Da) with a Na + ion. Additional mass ions identified in positive and negative ion mode were assigned as complexes of the MCS hexamer (n = 6) and octamer (n = 8) with Na + or with TFA À in various ratios. The dominant mass ion values of these active MCS factors from plants are also found in mass spectra of previously described endogenous digitalis-like factors (EDLF) from animals. This would suggest that ubiquitously distributed MCS factors may function as putative endogenous regulatory substances of Na,K-ATPase and possibly of other ATPases. With the symmetric display of several equivalent carbonyl or hydroxy groups, the structure of MCS factors is particularly suited for interactions with proteins and other bio-molecules. This could explain the high biological activity and the unusual properties of the MCS factors.

Mechanism of the Na,K-ATPase Inhibition by MCS Derivatives

“…It was furthermore remarked that these novel Na,K-ATPase inhibitors share many properties with putative endogenous digitalis-like factors (EDLF) (Kerek, 2000). Worth mentioning are identical mass ion values in mass spectra of MCS factors and the previously reported EDLFs, pH and concentration-dependent variations of their inhibitory activity, or sudden loss of activity that cannot be prevented by freezing (Kerek et al, 2002). Our recent findings confirmed all the previously reported spectral and ATPase enzyme inhibitory properties of MCS.…”

“…Mass spectrometric analyses support the proposal that MCS factors are capable of forming complexes with Na + or other cations (Kerek et al, 2002). The simulations of the reaction scheme presented above required an accounting of MCS-factor activation by H + , Na + or K + , as reflected by the respective terms in the equation for inhibitor activation (Eq.…”

“…MCS factors used in this study have been prepared according to the method described previously (Kerek et al, 2002). Very recently a simpler method of preparation has been accomplished and the previously assumed structure has been revised.…”

“…It was already reported that MCS factors are of inorganic nature and inhibit strongly not only the Na,K-ATPase but also the SR Ca-ATPase (Kerek, 2000, Kerek et al, 2002. In a systematic study, available ATPase preparations were tested in order to determine the range of inhibition.…”

“…We previously reported that the so-called MCS factors are of inorganic nature and strong inhibitors of the Na,K-ATPase and other P-type ATPases (Kerek et al, 2002). It was furthermore remarked that these novel Na,K-ATPase inhibitors share many properties with putative endogenous digitalis-like factors (EDLF) (Kerek, 2000).…”