title: Time-resolved thermodynamics: heat capacity change of transient species during photoreaction of PYP.
abstract: Heat capacity changes of short-lived transient species in different time ranges were measured for the first time by using the thermal component of the transient grating and transient lens signals at various temperatures. This method was applied to the transient intermediates of Photoactive Yellow Protein (PYP). The temperature dependence of the enthalpy change shows that the heat capacity of the short-lived intermediate pR2 (also called I1 or PYP(L)) species is the same as that of the ground state (pG) species within our experimental accuracy, whereas that of the long-lived intermediate pB (I2 or PYP(M)) is much larger (2.7 +/- 0.4 kJ/mol K) than that of pG. The larger heat capacity is interpreted in terms of the conformational change of the pB species such as melted conformation and/or exposure of the nonpolar residues to the aqueous phase. This technique can be used for photochemical reactions in general to investigate the conformational change and the hydrophobic interaction in a time domain.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Javaid Shahbaz
authors.initials: JS
authors.lastname: Khan
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imamoto
authors.forename: Mikio
authors.initials: M
authors.lastname: Kataoka
authors.forename: Fumio
authors.initials: F
authors.lastname: Tokunaga
authors.forename: Masahide
authors.initials: M
authors.lastname: Terazima
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D020607:Halorhodospira halophila / Q000737:chemistry; D007700:Kinetics; D010777:Photochemistry; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria