Time-resolved enthalpy changes of Sensory Rhodopsin II and the transducer complex during photo-reaction

The dynamics of protein emthalpy change of Natronobacterium pharaonis sensory rhodopsin II (NpSRII) and of NpSRII fused to the transducer (NpHtrII) truncated at 159 amino acid sequence form the N-terminus (NpSRII-$\delta$pHtrII) are investigated in solution phase at room temperature by the transient grating methods in real time. While kinetics of the photo-chemical reactions of both samples were similar to each other, significant difference was found in the molecular energy between NpSRII and NpSRII-$\delta$NpHtrII samples. The enthalpy of the second intermediate (L) of NpSRII-$\delta$NpHtrII is more stabilized compared with that of NpSRII. This stabilization indicates the influence of the transducer to the NpSRII structure in the early intermediate species by the complex formation