The Mitochondria Free Iron Content to Limit an Isotope Effect of 25Mg2+ in ATP Synthesis: A caution

Abstract

Sir: The Mg-promoted magnetic isotope effect (MIE), that is a nuclear spin selective over-activation of mitochondrial ATP synthesis by Mg nuclei, has been first discovered and originally described in a pioneer work by Buchachenko et al. [1] published in Cell Biochem. Biophys. back in 2005. Since then, a number of subsequent studies were uncovering some details of its ion–radical mechanism [2–5] with emphasize on potential medicinal applications due to both in vitro and in vivo experiments [6–9]. Obviously, a nuclear–magnetic control over the metal dependent enzymatic catalysis might be affected by traces of any other than Mg magnetic (paramagnetic, ferromagnetic) bivalent cations. In general, a possibility of the nucleotide phosphorylation dysfunctions caused by changes in intra-mitochondrial free metal cations pool was in fact ‘‘stated for alert’’ long ago [10]. As per the role of iron as a powerful suppressor for Mg-MIE in the nucleotidyl kinases directed ATP formation, this became clear just recently [5, 11]. Being attractive to pharmacologists [4, 6–8] and biotechnologists [12], Mg-MIE deserves to be specifically tested for its dependence on iron traces in situ. So we have investigated a correlation between the contents of free Fe in mitochondria isolated from several rat tissues (iron– lacking media employed), and the ATP synthesis rates estimated using these mitochondria in vitro respiration systems [13] in the presence of optimal (20 mM MgCl2) concentrations of either magnetic (Mg) or non-magnetic (Mg) ions [1, 3]. Both A grade isotopes with the enrichment level of not less than 96.4 % were purchased from Gamma Lab SA (Alicante, Spain). ATP synthesis rates were estimated by [p] orthophosphate (6.78–8.45 Ci/mmol, Amersham Radiochemical Centre, UK) incorporation in to de novo synthesized ATP [1] in the in vitro ‘‘breathing’’ mitochondria [13]. Mitochondria were isolated from the following rat tissues: spleen [14], liver [15], skeletal muscles [16], heart muscle [17], kidneys [18], and brain [19]. To get the intra– mitochondrial free iron pool samples, the pre-washed mitochondria pellets were first subjected to Triton X-100/ acetone treatment and then to a triple acetone–extraction of the total low molecular weight compounds fraction [1]. The resulting samples were used to measure the Fe content values by the energy–dispersive X-ray fluorescence spectrometry with a Fe–Zr performance element range employing the XEPOS–HE analytical system (SPECTRO Analytical Instruments, GmbH, Kleve, Germany). As seen from the data obtained (Table. 1), the endogenous mitochondrial-free iron pool level is no doubt critical for ‘‘turning on–off’’ the Mg-magnetic isotope effect expressing in a whole integrative (unbroken) mitochondria, i.e., within their ATP–synthesizing machinery. A. A. Svistunov Y. K. Napolov A. A. Bukhvostov (&) Department of Pharmacology, School of Pharmacy, I. M. Sechenov Moscow State Medical University, Moscow, Russia e-mail: tanzbukh@gmail.com