Magnetic isotope effect of magnesium in phosphoglycerate kinase phosphorylation

Abstract

Phosphoglycerate kinase (PGK) is found to be controlled by a 25 Mg 2؉ -related magnetic isotope effect. Mg 2؉ nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure 25 Mg 2؉ (nuclear spin 5͞2, magnetic moment ؉0.85) and 24 Mg 2؉ (spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of 25 Mg 2؉ , ATP production is 2.6 times higher compared with the yield of ATP reached in 24 Mg 2؉ -containing PGK-based catalytic systems. The chemical mechanism of this phenomenon is discussed. A key element of the mechanism proposed is a nonradical pair formation in which 25 Mg ؉ radical cation and phosphate oxyradical are involved. 25 Mg In one of their brilliant papers, Weber and Senior (1) pointed out that, despite great progress in our knowledge on the structure and our understanding of the molecular dynamics and functioning of ATP-synthesizing enzymes, the chemical mechanism of phosphorylation remains enigmatic: ''Our understanding of ATP synthesis remains rudimentary in molecular terms.'' Thus, our current understanding of ATP-synthesizing enzymes is still rudimentary at the molecular level and the key reaction responsible for the formation of the energy-carrying chemical bond POOOP remains obscure. Indeed, the structures of the protein parts and catalytic sites of phosphorylating enzymes, such as ATP synthase, creatine kinase, and phosphoglycerate kinase (PGK) (2-10), are well known. There is an understanding of their functioning as molecular rotary motors (referring to ATP synthase) or molecular pumps (creatine kinase, for instance); however, within the area of enzymatic reaction chemistry, all ideas are limited to speculations circulating mostly around nucleophilic mechanisms.An insight into the chemical mechanism follows from a recently discovered and remarkable phenomenon: a dependence of the phosphorylating activity of enzymes on Mg isotopy (11,12). This unusual effect was found for creatine kinase and ATP synthase (13). The rate of ATP production by enzymes in which the Mg 2ϩ ion has magnetic nucleus 25 Mg (nuclear spin, 5͞2; magnetic moment, Ϫ0.855 Bohr magneton) was shown to be two to three times higher than that induced by the same enzymes carrying spinless, nonmagnetic nuclei 24 Mg and 26 Mg. The discovery of this attention-catching isotope effect convincingly and unequivocally demonstrates that enzymatic phosphorylation is an ion-radical, electron-spin-selective process in which Mg ion Mg 2ϩ manifests itself as a reagent.The present study deals with our search for other examples of nuclear spin selectivity in biological processes. PGK (EC 2.7.11.08), a typical two-domain enzyme catalyzing the transfer of a phosphate group from ␣-phosphoglycerate to ADP, which leads to ATP production in eukaryotic cells (14), has been chosen for this purpose. Like creatine kinase, PGK contains Mg 2ϩ in its nu...

Reexamination of magnetic isotope and field effects on adenosine triphosphate production by creatine kinase

“…These enzymes are mitochondrial ATP synthase (8,11,16), phosphoglycerate kinase (9, 13), pyruvate kinase (12), and creatine kinase (9,12,15,20). The effects increased linearly with the amount of 25 Mg in the isotopic mixture (13). Furthermore, the activity of an enzyme that contains 25 Mg was strongly enhanced in the presence of the magnetic field.…”

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Are biochemical reactions affected by weak magnetic fields?

“…With no hypothetical mechanism to guide experimental design, the majority of these investigations have been, to varying degrees, unsatisfactory. A striking exception is a series of articles by Anatoly Buchachenko and Dmitry Kouznetsov (BK) and their associates (3)(4)(5)(6). In more than 10 papers dating back to 2005, including one in PNAS (3), BK have reported effects of magnetic interactions on the rate of enzymatic synthesis of ATP in vitro.…”

An experimental study of magnesium-isotope fractionation in chlorophyll-a photosynthesis

“…Recent studies by Buchachenko (2001), Buchachenko et al (2005aBuchachenko et al ( , 2005b, suggest a wholly different kinetic pathway that may involve coupling of the electron-and nuclear-spins in a free-radical reaction. The essence of this unconventional pathway is that decay of a transient free radical proceeds much faster (e.g.…”