Heat of hydrolysis of some phosphate compounds

The enzymatic hydrolysis of various phosphate compounds was carried out in an isothermic calorimeter. The following heats of reaction were found (average values): p-nitrophenyl phosphate, 4500 cal./mole; sodium pyrophosphate, 9000 cal./mole; POP bond of diphosphopyridine nucleotide, 13,000 cal./mole.