Abstract
The reductive tricarboxylic acid (rTCA) cycle is among the most plausible candidates for the first autotrophic metabolism in the earliest life. Extant enzymes fixing CO2 in this cycle contain cofactors at the catalytic centers, but it is unlikely that the protein/cofactor system emerged at once in a prebiotic process. Here, we discuss the feasibility of non-enzymatic cofactor-assisted drive of the rTCA reactions in the primitive Earth environments, particularly focusing on the acetyl-CoA conversion to pyruvate. Based on the energetic and mechanistic aspects of this reaction, we propose that the deep-sea hydrothermal vent environments with active electricity generation in the presence of various sulfide catalysts are a promising setting for it to progress. Our view supports the theory of an autotrophic origin of life from primordial carbon assimilation within a sulfide-rich hydrothermal vent.
Highlights
The non-enzymatic processing of the reductive tricarboxylic acid cycle-type carbon assimilation has been among the most challenging themes in the field of the origin of life [1,2,3,4].Various abiotic mechanisms to realize the reaction have been proposed, including the pyruvate formation from carbon monoxide (CO) and cyanide anion (CN− ) in the presence of Ni2+ [5], a high pressure condensation of alkyl thiols and formic acid to pyruvate catalyzed by FeS [6], and the photo-electrochemical CO32− − ∆ f G o (CO2) reduction and fixation into rTCA compounds on ZnS colloidal semiconductor under UV irradiation [7,8,9]
Various abiotic mechanisms to realize the reaction have been proposed, including the pyruvate formation from carbon monoxide (CO) and cyanide anion (CN− ) in the presence of Ni2+ [5], a high pressure condensation of alkyl thiols and formic acid to pyruvate catalyzed by FeS [6], and the photo-electrochemical CO2 reduction and fixation into rTCA compounds on ZnS colloidal semiconductor under UV irradiation [7,8,9]
In the biological rTCA cycle, CO2 fixation is operated by the two enzyme cofactors (Figure 1): thiamine pyrophosphate (TPP) assists the conversion of acetyl-CoA
Summary
The non-enzymatic processing of the reductive tricarboxylic acid (rTCA) cycle-type carbon assimilation has been among the most challenging themes in the field of the origin of life [1,2,3,4]. Various abiotic mechanisms to realize the reaction have been proposed, including the pyruvate formation from carbon monoxide (CO) and cyanide anion (CN− ) in the presence of Ni2+ [5], a high pressure condensation of alkyl thiols and formic acid to pyruvate catalyzed by FeS [6], and the photo-electrochemical CO2 reduction and fixation into rTCA compounds on ZnS colloidal semiconductor under UV irradiation [7,8,9] Their contributions to life’s origin have been questioned [10] because large discrepancies exist between the proposed mechanisms and the corresponding metabolic processes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
