Modeling the electron transport chain of purple non‐sulfur bacteria

Abstract

Purple non-sulfur bacteria (Rhodospirillaceae) have been extensively employed for studying principles of photosynthetic and respiratory electron transport phosphorylation and for investigating the regulation of gene expression in response to redox signals. Here, we use mathematical modeling to evaluate the steady-state behavior of the electron transport chain (ETC) in these bacteria under different environmental conditions. Elementary-modes analysis of a stoichiometric ETC model reveals nine operational modes. Most of them represent well-known functional states, however, two modes constitute reverse electron flow under respiratory conditions, which has been barely considered so far. We further present and analyze a kinetic model of the ETC in which rate laws of electron transfer steps are based on redox potential differences. Our model reproduces wellknown phenomena of respiratory and photosynthetic operation of the ETC and also provides nonintuitive predictions. As one key result, model simulations demonstrate a stronger reduction of ubiquinone when switching from high-light to low-light conditions. This result is parameter insensitive and supports the hypothesis that the redox state of ubiquinone is a suitable signal for controlling photosynthetic gene expression.

Overall energy conversion efficiency of a photosynthetic vesicle

“…Energy conversion through the quinone/quinol pool also involves electron exchange processes from outside the chromatophore as furnished, for example, through the enzymes NADH dehydrogenase and succinate dehydrogenase (Klamt et al, 2008).…”

“…The inner diameter of the vesicle is 50 nm. The model considered in this study is a variant of the one reported in (Cartron et al, 2014) In addition to ATP synthesis, the chromatophore utilizes the generated proton motive force also for NADH production via NADH dehydrogenase (Klamt et al, 2008) and, thereby, for control of the quinone/quinol pool redox state. Other channels for proton gradient depletion are flagellar motility (Kojadinovic et al, 2013) and proton leak across the vesicle membrane.…”

Network Identification and Flux Quantification of Glucose Metabolism in Rhodobacter sphaeroides under Photoheterotrophic H 2 -Producing Conditions

“…The use of the CO 2 -fixing CBB cycle for glucose catabolism leads to increased yields of pyruvate molecules from glucose. Although the CBB cycle dissipates ATP, it does not seem to be of major consequence since the cyclic photophosphorylation generates a huge amount of ATP (Ͼ10 mmol g Ϫ1 h Ϫ1 ), based on our calculation using the reported model of the electron transport chain of purple nonsulfur bacteria (24,40). Another big difference between the three catabolic routes is the formation of the reducing equivalents NADH and NADPH, partly because of the different directions of the GAPDH reaction (Fig.…”

“…In equation 5, 13 C is the natural abundance of 13 24 are pentose-5-P fragments 1 to 5 and oxaloacetate fragments 2 to 4, respectively. Ser 13 is the MDV of fragments 1 to 3 of serine.…”

Mathematical Models of Microbial Growth and Metabolism: A Whole-Organism Perspective

“…One good example is the model of bacterial metabolism, where the state variables are metabolite concentrations, gene expression levels, transcription factor activities, metabolic fluxes, and biomass concentration 25 . However, in many cases the aim is not to describe the whole organism but instead to focus on specific subsystems of the cell, such as the assembly of the Z-ring 37 , or the electron transport chains of mitochondria 51 and purple non-sulfur bacteria 52 . Depending on the specific properties of the given biological network under consideration, different formalisms can be employed to simulate its dynamic behaviour.…”