CoC bond dissociation energy and reaction volume change of 2′,5′-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry

Abstract

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B 12 analog 2′,5′-dideoxyadenosylcobalamin, which lacks an OH group at the 2′ position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Φ d (0.25±0.02), CoC bond dissociation energy (BDE; 31.8±2.5 kcal mol −1) and reaction volume change ΔV R (6.5±0.5 ml mol −1) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the CoC bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.