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Role of water activity on the rates of acetyl phosphate and ATP hydrolysis
Author(s) -
de Meis Leopoldo,
Suzano Valdecir Antunes
Publication year - 1988
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(88)80389-2
Subject(s) - chemistry , hydrolysis , dimethyl sulfoxide , phosphate , atp hydrolysis , ethylene glycol , solvent , reaction rate constant , inorganic chemistry , atpase , hydrolysis constant , medicinal chemistry , nuclear chemistry , organic chemistry , kinetics , enzyme , physics , quantum mechanics
The rates of hydrolysis of acetyl phosphate in the presence of 0.1 M NaOH and of ATP in the presence of either 1 M HCl or 1 M NaOH were measured at different temperatures and in the presence of different concentrations of the organic solvents dimethyl sulfoxide or ethylene glycol. Under all conditions tested, there was a progressive increase in the rate constant of hydrolysis of both phosphate compounds as the water activity of the medium was decreased by the addition of organic solvents. At 25°C, substitution of 70% of the water of the medium by dimethyl sulfoxide promoted an increase of two orders of magnitude in the rate constant of acetyl phosphate hydrolysis. In the presence of 80% and 90% dimethyl sulfoxide the rate of acetyl phosphate hydrolysis increased by more than two orders of magnitude and was so fast that it could not be measured with the method used. The effect of organic solvents on the rate of ATP hydrolysis was less pronounced than that observed for acetyl phosphate hydrolysis. At 30°C, substitution of 90% of water by an organic solvent promoted a 4–6‐fold increase of the rate of ATP hydrolysis. Acceleration of either acetyl phosphate or ATP hydrolysis rates was promoted by a decrease in both activation energies ( E a ) and in entropies of activation Δ S ‡. The data obtained are discussed with reference to the mechanism of catalysis of enzymes involved in energy transduction such as the Ca 2+ ‐ATPase of sarcoplasmic reticulum and the F 1 ‐ATPase of mitochondria.