LASER-INDUCED PHOTOACOUSTIC CALORIMETRIC DETERMINATION OF ENTHALPY AND VOLUME CHANGES IN PHOTOLYSIS OF 5'-DEOXYADENOSYLCOBALAMIN AND METHYLCOBALAMIN

Photolysis of 5'-deoxy-5'-adenosylcobalamin (AdoCbl) in neutral aqueou s solution and methylcobalamin (MeCbl) in neutral and acid aqueous sol ution has been investigated using pulsed, time-resolved photoacoustic calorimetry in the temperature range 10-30 degrees C. The enthalpy cha nges for the above cobalamins, 129 +/- 17, 163 +/- 21 and 176 +/- 23 k J mol(-1), respectively, are consistent with the values obtained by th ermolytic kinetic methods. The reaction volume changes for them, 6 +/- 1, 2 +/-: 0.5 and 5 +/- 1 mi mol(-1), respectively, are probably due to the conformational changes of the corrin ring and its side chains a ccompanying Co-C bond cleavage.