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Abstract:
The total reaction enthalpy change ∆rH associated with the carboxylation and oxygenation of D-ribulose 1,5-bisphosphate (RuBP) catalysed by RUBISCO from spinach and Rhodospirillum rubrum was measured for the first time with sensitive microcalorimetry. The enthalpy changes ∆r,cH and ∆r,oH associated with the carboxylase and oxygenase reactions were determined separately using the known ratio of these reactions.
∆r,cH and ∆r,oH corrected for the heat of neutralisation due to proton release during the overall carboxylation
or oxygenation processes. For the corrected enthalpy change ∆r,cH` of the carboxylase reaction catalysed by RUBISCO of spinach a value of -21.34±0.4 kJ mol-1 was determined. In the case of the oxygenase reaction for RUBISCO of spinach a reaction enthalpy change ∆r,oH`of -319.1±9.6 kJ mol-1 which is typical for energy rich reactions, was found. This value is comparable with ∆r,oH´=-291.4±5.8 kJ mol-1 with the oxygenase reaction catalysed by Co2+-activated RUBISCO from R. rubrum.
