Synthesis and breakdown of universal metabolic precursors promoted by iron

Abstract

Life builds its molecules from CO2 and breaks them down to CO2 again through the intermediacy of just five metabolites that act as the hubs of biochemistry.1 However, how core biological metabolism initiated and why it uses the intermediates, reactions and pathways that it does remains unclear. Here, we describe a purely chemical reaction network promoted by Fe2+ in which aqueous pyruvate and glyoxylate, two products of abiotic CO2 reduction,2–4 build up nine of the eleven Krebs (tricarboxylic acid, TCA) cycle intermediates, including all five universal metabolic precursors. The intermediates simultaneously break down to CO2 in a life-like regime resembling biological anabolism and catabolism.5 Adding hydroxylamine6–8 and Fe0 into the system produces four biological amino acids in a manner paralleling biosynthesis. The observed network significantly overlaps the Krebs and glyoxylate cycles9,10 and may represent a prebiotic precursor to these core metabolic pathways.

A thermodynamic atlas of carbon redox chemical space

“…It would be particularly interesting to include carboxylation and decarboxylation reactions (both reductive/oxidative and non-reductive/non-oxidative), which would effectively connect the different n-carbon redox chemical spaces to each other, but would significantly increase the complexity of the analysis. In addition, including additional types of reactions such as aldol/retro-aldol reactions and hydrations/dehydrations would fully map the chemical space model to experimentally tractable reaction networks 25,[64][65][66] .…”

“…This potential (electron donor) E could represent that set by a steady state ratio of NAD + /NADH or other abundant redox cofactor inside the cell 23 . Alternatively, in the context of prebiotic chemistry, it could represent the potential associated to a given concentration of molecular hydrogen in an alkaline hydrothermal vent or different iron oxidation states in prebiotic oceans 24,25 . Given a value of , we convert the of each reaction into a Gibbs reaction energy, using A notable finding of this analysis is that, across a range of cofactor potentials, metabolites in 4-carbon linear-chain redox chemical space have on average significantly lower relative Gibbs energies than the non-biological compounds ( Fig 3B).…”

Photosynthesis on exoplanets and exomoons from reflected light

“…Of these five networks, the two most important are the reverse tricarboxylic acid (rTCA) cycle and the Wood-Ljungdahl pathway. A combination of physiological, genomic and bioenergetic arguments have been marshalled (Smith and Morowitz, 2016;Weiss et al, 2018;Nunoura et al, 2018) in conjunction with promising laboratory experiments (Muchowska et al, 2017;Varma et al, 2018;Muchowska et al, 2019) to suggest these pathways were the first to emerge on Earth; in fact, certain proposals hypothesize that a hybrid of these two networks might have constituted the ancestral metabolic pathway (Braakman and Smith, 2012;Camprubi et al, 2017).…”

On the Likelihood of Life Originating

“…How abundant is life in the universe? A stunning new Nature publication indirectly illuminates this problem . The question is heavily debated because with just one example, there is a broad range of uncertain answers (from profuse to extremely rare).…”

“…A stunning new Nature publication indirectly illuminates this problem. [1] The question is heavily debated because with just one example, there is a broad range of uncertain answers (from profuse to extremely rare). It is noteworthy that in the Drake equation (a very rough estimation of numbers of hypothetical extraterrestrial civilizations in our galaxy), f l (the fraction of Earth-like planets giving rise to life) was presumed to be very close to 1.…”