Analysis of the Intermediary Metabolism of a Reductive Chemoautotroph

摘要

All extant life forms depend, directly or indi-rectly, on the autotrophic fixation of the dominant elements of the biosphere: carbon, hydrogen, nitrogen, oxygen, phos-phorus, and sulfur. We have earlier presented the canonical network of reactions that constitute the anabolism of a reductive chemoautotroph. Separating this network into subgraphs reveals several empirical generalizations: (1) ac-etate (acetyl-CoA), pyruvate, phosphoenol pyruvate, ox-aloacetate, and 2-oxoglutarate serve as universal starting points for all pathways leading to the universal building blocks-20 amino acids and 4 ribonucleotide triphosphates; (2) all pathways are anabolic; (3) all reactions operate by complete utilization of outputs with no molecules left be-hind as waste, ensuring conservation of information; (4) the core metabolome of 120 compounds is acidic, consisting of compounds containing phosphoric or carboxylic acid or both; and (5) the core network is both brittle-vulnerable to a single break-and robust-having persisted for 4 billion years. Preliminary analysis of the chemical reactions and resultant structures reveals (a) a sparseness among possible molecular structures; (b) subdomains in the network; and (c) restriction of anabolism to a small set of rudimentary or-ganic reactions with limited diversity in chemical mecha-nisms. These generalizations have implications for biogen-esis and trophic ecology.