Experimental evidence for multistability in a photobiochemical system

Abstract

The kinetic behavior of a typical Hill reaction catalyzed by thylakoids and using the oxidized form of 2,6-dichloroindophenol (DCPIPox) as the artificial clectron acceptor, is considered. Here, the light absorption process and the reduction of DCPlPox are autocatalytically coupled, leading to the occurrence of rnultiplc steady states with respect to either the acceptor concentration or the incident light intensity. Experimental evidence is prescntcd for both cases and the emergence of autocatalysis is discussed. The effect of the spatial arrangment on the global behavior of the system described is emphasized.Biocatalytic reactions have bcen studied almost enlerely from the viewpoint of their time-dependent behavior. Rcccntly, a more relevant and realistic approach has consisted of coupling purely catalytic functions with various phenomena intrinsically linked to space, such as diffusion, partition of metabolites, vectorial processes and convection. When autocatalytic reactions are considered, qualitatively different behavior of the system has been predicted theoretically, for example multistability and/or spatiotcniporal structure formation [I]. Experimental evidence of multistability for either ki nctic or electrochemical memory in diffusion-reaction coupled and reconstitutcd enzyme systems has been reported [2 -51. Nevertheless, in the framework of this spatiotemporal concept, littlc attention has been paid to radiation phenomena which, likc diffusion. are also essentially space-dependent and whose role is fundamental in numerous chemical and biochemical processes. A thorough theoretical analysis considcring a simple photodependent isomerization reaction in which one of the isomers absorbs light and restores this energy to the system in the form of heat, was published by Nitzan et al. 16, 71. Here, the light absorption process and the increase of the system's temperature become autocatalytically coupled, leading to the occurrence of multiple steady states and hysteresis. The latter predictions have been experimentally confirmed in the case of the N 0 2 / N 2 0 4 dissociation reaction [8] and more recently in the S03F/S206F2 system [9]. As far as we are aware, no experimental examination of the phenomena pertaining the biological photoreactions has been yet attemped.In the present work, chloroplast thylakoids are immobilized [lo-121 in an artificial membrane lying on the bottom of a reactor fed with DCPIPox as the electron acceptor. The DCPl Pox species adsorbs strongly within the range of illumi- Ahhrc~viutions. DCPIPox, oxidized form of the 2,6-dichloroindophenol. nation wavelengths. Under such conditions we show that thc association between the purely photoassisted reduction of the DCPIPox, and its absorption by light intensity in the range of 600 -800 nm, leads to the appearance of an autocatalytic effect in the rate of reaction. More precisely, the yield of the photoreaction first increases and then decreases. as the DCPIPox concentration increases. The coupling of this nonlinear reaction term with a tra...

Spatial patterns in a photobiochemical system

“…According to the reaction-diffusion theory, the interaction of diffusion transport and nonlinear chemical kinetics can lead to instabilities of a concentration field with the result that initially homogeneous domains develop regional nonuniformities (1,2). The autocatalytic nature of a photobiochemical reaction resulting from the coupling of two intrinsically linear processes-i.e., the reduction of DCIP by thylakoids and the light absorption by the same electron acceptor DCIP-has been demonstrated in a spatially compartmentalized system (25,30). In those studies, the existence of multiple steady states in a single open reactor and of stable asymmetric steady states in coupled open reactors with mutual diffusion through an inert membrane was shown by experimental and numerical methods.…”

“…Similar one-dimensional patterns were also observed when red (cutoffofradiation <580 nm; wavelengths ofphotosystem II excitation) and infrared filters were utilized together. The chlorophyll concentration and light intensity determinations were done as reported (25).…”

“…Similar one-dimensional patterns were also observed when red (cutoffofradiation <580 nm; wavelengths ofphotosystem II excitation) and infrared filters were utilized together. The chlorophyll concentration and light intensity determinations were done as reported (25).Patterns in Gelled Medium. For the experiment conducted in a polyacrylamide gel, 3.5% (wt/vol) acrylamide monomer, 0.0875% N,N'-methylenebisacrylamide, 0.3% N,N,N',N'-tetramethylethylenediamine (TEMED), and 0.08% ammonium persulfate were added to the thylakoid suspension.…”

Pattern formation in an immobilized bienzyme system. A morphogenetic model

“…This latter transition emerges when the non-linear properties of the implicated reactions are coupled to diffusion under welldefined boundary conditions. It has been suggested that the coupling ofthe non-linear photosynthetic reduction ofan electron acceptor [23] to diffusion in the presence of a gradient was the underlying mechanism of the symmetry change of the electron acceptor in a photobiochemical system [13].…”

Multiple steady states and dissipative structures in a circular and linear array of three cells: Numerical and experimental approaches

“…The biochemical processes taking place in each cell are identical to those described by Breton et ai. 29 ,30 and the evolution of the substrate is governed by Eq. (1).…”