Energetics and Volume Changes of the Intermediates in the Photolysis of Octopus Rhodopsin at a Physiological Temperature

Abstract

Enthalpy changes (Delta H) of the photointermediates that appear in the photolysis of octopus rhodopsin were measured at physiological temperatures by the laser-induced transient grating method. The enthalpy from the initial state, rhodopsin, to bathorhodopsin, lumirhodopsin, mesorhodopsin, transient acid metarhodopsin, and acid metarhodopsin were 146 +/- 15 kJ/mol, 122 +/- 17 kJ/mol, 38 +/- 8 kJ/mol, 12 +/- 5 kJ/mol, and 12 +/- 5 kJ/mol, respectively. These values, except for lumirhodopsin, are similar to those obtained for the cryogenically trapped intermediate species by direct calorimetric measurements. However, the Delta H of lumirhodopsin at physiological temperatures is quite different from that at low temperature. The reaction volume changes of these processes were determined by the pulsed laser-induced photoacoustic method along with the above Delta H values. Initially, in the transformation between rhodopsin and bathorhodopsin, a large volume expansion of +32 +/- 3 ml/mol was obtained. The volume changes of the subsequent reaction steps were rather small. These results are compared with the structural changes of the chromophore, peptide backbone, and water molecules within the membrane helixes reported previously.

Photochemical Intermediates of Arabidopsis Phototropin 2 LOV Domains Associated with Conformational Changes

“…The principle underlying these measurements has been reported. 27,28,50 Here we here describe briefly our methods.…”

“…Alternatively, the TrL [25][26][27][28] or photo-acoustic (PA) techniques [29][30][31] combined with the temperature dependence method or solvent variation method have sometimes been used to determine the enthalpy change (ΔH) and the volume change (ΔV) of irreversible reactions. However, it was unavoidable to use an assumption that these thermodynamic properties do not depend on the temperature or solvent.…”

A Purified Agonist-Activated G-Protein Coupled Receptor: Truncated Octopus Acid Metarhodopsin

“…The photoproduct's ability to stimulate GTP γ S-binding by added G q decreased in a time-dependent manner (minute to hour). The life time of Transient Acid Metarhodopsin is so fast (180 µ s) (Nishioku et al ., 2002), that it probably is not a factor in our experiments but it is possible that it is in equilibrium with t-Acid Metarhodopsin. Since the measured differences between the two types of Acid Metarhodopsin are small (Zhang et al ., 1997), even if the transient species is important we believe it must have a structure close to that of t-Acid Metarhodopsin.…”

Crystallographic Analysis of the Primary Photochemical Reaction of Squid Rhodopsin

“…It has been reported that a similar energy (35 kcal/mol) is stored in Batho for vertebrate and invertebrate rhodopsins. 12,13,29,30 This similarity can be understood by supposing that the configuration of the retinal in Batho is conserved among these rhodopsins. However, this does not necessarily mean that excited-state dynamics are also similar for these rhodopsins.…”