title: Quantitative mathematical expressions for accurate in vivo assessment of cytosolic [ADP] and DeltaG of ATP hydrolysis in the human brain and skeletal muscle.
abstract: Magnetic Resonance Spectroscopy affords the possibility of assessing in vivo the thermodynamic status of living tissues. The main thermodynamic variables relevant for the knowledge of the health of living tissues are: DeltaG of ATP hydrolysis and cytosolic [ADP], the latter as calculated from the apparent equilibrium constant of the creatine kinase reaction. In this study we assessed the stoichiometric equilibrium constant of the creatine kinase reaction by in vitro (31)P NMR measurements and computer calculations resulting to be: logK(CK)=8.00+/-0.07 at T=310 K and ionic strength I=0.25 M. This value refers to the equilibrium: PCr(2-)+ADP(3-)+ H(+)=Cr+ATP(4-). We also assessed by computer calculation the stoichiometric equilibrium constant of ATP hydrolysis obtaining the value: logK(ATP-hyd)=-12.45 at T=310 K and ionic strength I=0.25 M, which refers to the equilibrium: ATP(4-)+H(2)O=ADP(3-)+PO(4)(3-)+2H(+). Finally, we formulated novel quantitative mathematical expressions of DeltaG of ATP hydrolysis and of the apparent equilibrium constant of the creatine kinase reaction as a function of total [PCr], pH and pMg, all quantities measurable by in vivo (31)P MRS. Our novel mathematical expressions allow the in vivo assessment of cytosolic [ADP] and DeltaG of ATP hydrolysis in the human brain and skeletal muscle taking into account pH and pMg changes occurring in living tissues both in physiological and pathological conditions.
authors.affiliation: Biochimica Clinica, Dipartimento di Medicina Clinica e Biotecnologia Applicata "D. Campanacci", Università di Bologna, Via Massarenti, 9, 40138 Bologna, Italy. stefano.iotti@unibo.it
authors.forename: Stefano
authors.initials: S
authors.lastname: Iotti
authors.forename: Chiara
authors.initials: C
authors.lastname: Frassineti
authors.forename: Antonio
authors.initials: A
authors.lastname: Sabatini
authors.forename: Alberto
authors.initials: A
authors.lastname: Vacca
authors.forename: Bruno
authors.initials: B
authors.lastname: Barbiroli
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008274:Magnesium / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D008274:Magnesium