Comprehensive Analyses of the Enhancement of Oxygenesis in Photosynthesis by Bicarbonate and Effects of Diverse Additives: Z-scheme Explanation versus Murburn Model

Abstract

The Z-scheme electron transport chain (ETC) explanation for photosynthesis starts with the serial/sequential transfer of electrons sourced from water molecules bound at Photosystem II via a deterministic array of redox centers (of various stationary/mobile proteins), before \"sinking\" via the reduction of NADP+ bound at flavin-enzyme reductase. Several research groups’ finding that additives (like bicarbonate) enhance the light reaction had divided the research community because it violated the Z-scheme. The untenable aspects of the Z-scheme perception were demonstrated earlier and a murburn bioenergetics (a stochastic/parallel paradigm of ion-radical equilibriums) model was proposed to explain photophosphorylation and Emerson effect. Herein, we further support the murburn model with accurate thermodynamic calculations, which show that the cost of one-electron abstraction from bicarbonate [491 kJ/mol] is lower than water [527 kJ/mol]. Further, copious thioredoxin enables the capture of photoactivated electrons in milieu, which aid in the reduction of nicotinamide nucleotides. The diffusible reactive species (DRS) generated in milieu sponsor phosphorylations and oxygenic reactions. With structural analysis of Photosystems and interacting molecules, we chart out the equations of reactions that explain the loss of labeled O-atom traces in delocalized oxygenesis. Thus, this essay discredits the Z-scheme and explains key outstanding observations in the field.

Murburn concept in cellular function and bioenergetics, Part 1: Understanding murzymes at the molecular level

“…Kok-Joliot cycle was invented to obviate the formation of DROS but the fact is that chloroplasts show copious DROS and it also fails to explain why oxygen evolution is seen with the excitation of PS II!  The Z-scheme & Kok-Joliot cycle paradigm cannot explain Radmer & Stemler groups' findings of oxygenesis-enhancement with bicarbonate and the incorporation of bicarbonate's O atom in the evolved oxygen and carbon dioxide (53)(54).…”

“…Therefore, there is no issue in bicarbonate serving as e-source in physiological photosynthesis, under the murburn purview. Further, murburn model involving DROS could also explain the dynamics and lower availability of heavy-labeled 18 O atom of bicarbonate in oxygen evolved (54). Most importantly, in the stochastic murburn model, there is no limitation on the number of photons absorbed or used for generating DROS, neither is there any fixed stoichiometry.…”

Synthesis of theories on cellular powering, coherence, homeostasis and electro‐mechanics: Murburn concept and evolutionary perspectives

“…With reference to mitochondrial oxidative phosphorylation, this proposal vouches that some of the “electron transport chain” (ETC) proteins (Complexes I, III, and IV) serve as proton pumps, leading to the establishment of “pmf“ consisting of a chemical pH gradient and an electrical trans‐membrane potential (TMP), which in turn, enables “CRAS” by Complex V. We had provided elaborate critique of the pmf ‐based explanation for bioenergetics (Manoj, 2018a, 2018b) and proposed an idea in lieu called murburn concept. The insights derived from murburn concept were applied to explain the observations in various core physiologies involving oxygen (Manoj, Gideon, & Jaeken, 2022a CBI; Manoj & Gideon, 2022), such as: xenobiotic metabolism and anomalous dose responses (Manoj, Parashar, Gade, et al 2016; Parashar & Manoj, 2021; Parashar et al, 2018), aerobic respiration, thermogenesis and homeostasis (Manoj & Bazhin, 2021; Manoj et al, 2018; Manoj, Bazhin, Tamagawa, et al, 2022; Manoj, Parashar, et al, 2019; Manoj, Ramasamy, et al, 2020; Manoj, Soman, et al, 2019), photo‐transduction in vision (Manoj & Jacob, 2020; Manoj, Tamagawa, et al, 2022), oxygenic photosynthesis (Gideon et al, 2020; Manoj, Bazhin, Jacob, et al, 2022, Manoj, Bazhin, Wu, et al, 2022; Manoj, Gideon, et al, 2020; Manoj, Gideon, Parashar et al, 2022; Manoj, Gideon, & Jaeken, 2022b; Manoj & Manekkathodi, 2021; Manoj, Manekkathodi, et al, 2022; Manoj, Tamagawa, et al, 2022), ionic differentials and electrophysiology (Manoj, Bazhin, & Tamagawa, 2021; Manoj, Gideon, Bazhin, et al, 2022; Manoj & Tamagawa, 2021; Manoj, Tamagawa, et al, 2022), and so on. In the context of aerobic respiration or oxygenic photosynthesis, the murburn model advocates that DRS produced during oxidation of NAD(P)H activates ADP/Pi producing ADP* and/or Pi* radicals, which spontaneously react for the direct formation of phospho‐anhydride/phospho‐ester (ATP), as it is the case we demonstrated in vitro (Manoj, Parashar, et al, 2019; Manoj, Ramasamy, et al, 2020).…”

Murburn posttranslational modifications of proteins: Cellular redox processes and murzyme‐mediated metabolo‐proteomics

“…( In the context of this review, it is to be registered that all PTMs result from BET/BMT, whether resulting from classical affinity‐driven enzyme activity or murzyme‐based murburn activity .) Murburn concept advocates an opportunistic “source‐to‐sink trafficking” of electrons (which may lead to the commissioning of “useful work”), as opposed to the earlier improbable and deterministic ideas like “electron transport chain (ETC)” (Manoj, 2018b; Manoj, 2020a,b,c; Manoj, Bazhin, Parashar, et al, 2022). The new awareness has explained that the actual role of oxygen in life is to generate DRS and enable ECS (Manoj et al, 2022a).…”