[Properties of the high energy phosphate bonds of triphosphoinositide]

High heat of enzymatic hydrolysis of triphosphoinositide phosphate bonds and of high-energy phosphates is observed using microcalorimetry. Heats of hydrolysis of triphosphoinositide, ADP and ATP sharply increase with increasing pH values from 6.6 to 7.4. Heat of hydrolysis of diphosphoinositide correlates with that of low-energy phosphates, pK4 and pK5 values for triphosphoinositide are found to be 7.4 and 9.3 respectively by means of potentiometric titration deltaGo' values for diphosphoinositide and triphosphoinositide are -3.5 and -7.1 kcal/mole respectively, taking into consideration the correction for heat neutralization-ionization during hydrolysis. Rapid triphosphoinositide hydrolysis takes place in 1% aqueous pyridine solution at 100 degrees C. In contrast to diphosphoinositide and monophosphoinositide, infrared spectra of triphosphoinositide have an additional absorption band at 930 cm(-1). 31P NMR method has revealed the presence of one diester and two monoester groups in the molecule of triphosphoinositide. The differences described between triphosphoinositide and other compounds with phosphomonoester groups are suggested to be due to electrostatic nonbounded interaction of vicinal diequatorial phosphate groups.