NON-ENZYMIC HYDROLYSIS OF ATP - INFRARED INVESTIGATIONS OF INTER-MOLECULAR INTERACTIONS

The nonenzymic hydrolysis of {A figure is presented} and {A figure is presented} were studied by infrared (IR) spectroscopy. Protons resulting from hydrolysis of ATP are not bound to the N1 atoms of the adenine residues. With hydrolysis of {A figure is presented}, these protons are partially bound to the terminal phosphate group of ADP, namely, {A figure is presented}, {A figure is presented}, {A figure is presented}, and {A figure is presented}, present after hydrolysis. With decreasing pH or when Mg2+ ions are present, all hydrolysis protons are attached to the orthophosphate molecules. With hydrolysis of {A figure is presented} the pH decreases up to 40% degree of hydrolysis. Then the system becomes self-buffered in the physiological pH region. A similar pH decrease is found with hydrolysis of {A figure is presented}. With these systems, however, the pH decreases slightly also at degrees of hydrolysis larger than 40%. No other systems show pronounced pH changes during hydrolysis; in other words, they are buffer systems. The IR bands demonstrate that mesomeric bond resonance in the phosphate groups strongly depends on whether protons are present at these groups. Regarding the equilibria of proton attachment mentioned above, mesomeric bond resonance in these groups strongly depends on pH and on the presence of {A figure is presented} ions. With hydrolysis of ATP, two POH groups are formed that bind H2O molecules via strong hydrogen bonds, changing the solvate structure. Finally, easily polarizable hydrogen bonds are formed, for instance, {A figure is presented} bonds with the hydrolysis of {A figure is presented}, and {A figure is presented} bonds with the hydrolysis of {A figure is presented}. These bonds strongly interact with their environment. The formation of these hydrogen bonds strongly depends on pH and the presence of {A figure is presented} ions. All these effects, especially the intermolecular ones, contribute to the change of free energy during ATP hydrolysis. © 1979.