Temperature-Driven Changeover in the Electron-Transfer Mechanism of a Thermophilic Plastocyanin

Abstract

Electron-transfer kinetics of the thermophilic protein Plastocyanin from Phormidium laminosum adsorbed on 1,ω-alkanedithiol self-assembled monolayers (SAMs) deposited on gold have been investigated. The standard electron-transfer rate constant has been determined as a function of electrode-protein distance and solution viscosity over a broad temperature range (0-90 °C). For either thin or thick SAMs, the electron-transfer regime remains invariant with temperature, whereas for the 1,11-undecanethiol SAM of intermediate chain length, a kinetic regime changeover from a gated or friction-controlled mechanism at low temperature (0-30 °C) to a nonadiabatic mechanism above 40 °C is observed. To the best of our knowledge, this is the first time a thermal-induced transition between these two kinetic regimes is reported for a metalloprotein.

Mechanism of Formation of Copper(II) Chloro Complexes Revealed by Transient Absorption Spectroscopy and DFT/TDDFT Calculations

“…As shown in the previous studies, a [ ) tetrachloro complexes agree with the steady-state spectra, Figure 1 and Table 2. Similarly to copper(II) chloro complexes, tetraethylammonium chloride species, which are the source of chloride ions, are present as NEt 4 + Cl − ion pairs in dichloromethane solutions and as fully separated ions in acetonitrile solutions (association constants, K a = 12 and 92 000 M 2− complexes in the LMCT excited states. Indeed, quantum yields of the formation of copper(I) complexes, products of the radical dissociation do not exceed 0.5% 32,44 and are significantly smaller than quantum yields of the formation of the ionic dissociation products.…”

“…The induced absorption bands decays to zero concurrently with recovery of the groundstate bleach and without any spectral reshaping. The decay of the ΔA bands is single-exponential, ΔA(t) = ΔA 0 ·e −k obs t (Figure 4 and 5), where the pseudo-first-order rate constant (k obs ) is found to linearly depend on the concentration of NEt 4 Cl, k obs = k q · [NEt 4 Cl], Figure 6. On the basis of the k obs values resulting from these single-exponential fits, the bimolecular rate constants, k q , are evaluated to be (9.0 ± 0.1) × 10 The Journal of Physical Chemistry B Article Diffusion-Controlled Rate Constants.…”

“…It is well-known that copper plays an important role in metabolism of living organisms, for example, plastocyanin takes part as an electron donor species in the photosynthesis of the photosystem I in plants and bacteria . Electron and energy transport processes of this and several other copper-containing proteins have been the focus of many recent studies. − In general, these transfer properties are associated with the ability of a copper ion to change its oxidation number reversibly . However, plastocyanin is a rather complicated system for studying the photoinduced transformation of the copper proteins.…”

Protein crosslinking improves the thermal resistance of plastocyanin immobilized on a modified gold electrode

“…showing thus an improved thermal resistance. Nevertheless, it should be noted that the = -54 ± 3 kJ mol -1 , are less negative than those obtained when the protein was adsorbed on either graphite [12] or alkyldithiol monolayers [22], suggesting a tighter protein structure upon adsorption on cysteamine monolayers, that requires a smaller solvent reorganization upon changing the redox state. This finding indicates that the formation of intra-and inter-protein amide bonds in the crosslinked film seems to not affect the integrity and functionality of the copper redox centers.…”