Magnesium isotope effects in enzymatic phosphorylation.
Recent discovery of magnesium isotope effect in the rate of enzymatic synthesis of adenosine triphosphate (ATP) offers a new insight into the mechanochemistry of enzymes as the molecular machines. The activity of phosphorylating enzymes (ATP-synthase, phosphocreatine, and phosphoglycerate kinases) in which Mg(2+) ion has a magnetic isotopic nucleus 25Mg was found to be 2-3 times higher than that of enzymes in which Mg(2+) ion has spinless, nonmagnetic isotopic nuclei 24Mg or 26Mg. This isotope effect demonstrates unambiguously that the ATP synthesis is a spin-dependent ion-radical process. The reaction schemes, suggested to explain the effect, imply a reversible electron transfer from the terminal phosphate anion of ADP to Mg(2+) ion as a first step, generating ion-radical pair with singlet and triplet spin states. The yields of ATP along the singlet and triplet channels are controlled by hyperfine coupling of unpaired electron in 25Mg+ ion with magnetic nucleus 25Mg. There is no difference in the ATP yield for enzymes with 24Mg and 26Mg; it gives evidence that in this reaction magnetic isotope effect (MIE) operates rather than classical, mass-dependent one. Similar effects have been also found for the pyruvate kinase. Magnetic field dependence of enzymatic phosphorylation is in agreement with suggested ion-radical mechanism.
Buchachenko
Anatoly L
AL
N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 119991 Moscow, Russia. abuchach@chph.ras.ru
Kouznetsov
Dmitry A
DA
Breslavskaya
Natalia N
NN
Orlova
Marina A
MA
D000255:Adenosine Triphosphate / Q000378:metabolism; D004583:Electrons; D006868:Hydrolysis / Q000187:drug effects; D007554:Isotopes / Q000737:chemistry / Q000494:pharmacology; D008274:Magnesium / Q000737:chemistry / Q000494:pharmacology*; D008928:Mitochondria / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010770:Phosphotransferases / Q000378:metabolism*
D007554:Isotopes; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D008274:Magnesium