Studies on luciferase from Photobacterium phosphoreum. X. Heat of formation of the intermediate in the bioluminescent reaction studied by stopped-flow calorimetry.

The heat production in the reaction of luciferase-FMNH2 complex with O2 in the absence of aldehyde was measured by stopped-flow calorimetry. deltaH of the reaction, luciferase-FMNH2+ O2 leads to intermediate X1, is -1.3 X 10(2) kJ.mol-1 and the calculated deltaS for the reaction is -180 J.mol-1.K-1 at 20 degrees C. The heat production in the bioluminescent reaction was also measured in the presence of a saturating concentration of aldehyde, and it was estimated that 43 and 79% of the C10 and C13 aldehydes, respectively, bound with the intermediate X1 are converted to carboxylic acid yielding energy for photon emission.