Computational identification of obligatorily autocatalytic replicators embedded in metabolic networks

Ádám Kun¹^,2 , Balázs Papp³^,5 and Eörs Szathmáry¹^,2^,4

¹Collegium Budapest, Institute for Advanced Study, Szentháromság utca 2, Budapest H-1014, Hungary

²Department of Plant Taxonomy and Ecology, Institute of Biology, Eötvös University, Pázmány Péter sétány 1/C, Budapest H-1117, Hungary

³Faculty of Life Sciences, The University of Manchester, Oxford Road, Manchester M13 9PT, UK

⁴Parmenides Center for the Study of Thinking, Kardinal Faulhaber Strasse, Munich D-80333, Germany

⁵Current address: Institute of Biochemistry, Biological Research Center, Szeged H-6701, Hungary

author email corresponding author email

Genome Biology 2008, 9:R51doi:10.1186/gb-2008-9-3-r51


Published:	10 March 2008

Subject areas: Molecular biology, Evolution, Genetics

Abstract

Background

If chemical A is necessary for the synthesis of more chemical A, then A has the power of replication (such systems are known as autocatalytic systems). We provide the first systems-level analysis searching for small-molecular autocatalytic components in the metabolisms of diverse organisms, including an inferred minimal metabolism.

Results

We find that intermediary metabolism is invariably autocatalytic for ATP. Furthermore, we provide evidence for the existence of additional, organism-specific autocatalytic metabolites in the forms of coenzymes (NAD⁺, coenzyme A, tetrahydrofolate, quinones) and sugars. Although the enzymatic reactions of a number of autocatalytic cycles are present in most of the studied organisms, they display obligatorily autocatalytic behavior in a few networks only, hence demonstrating the need for a systems-level approach to identify metabolic replicators embedded in large networks.

Conclusion

Metabolic replicators are apparently common and potentially both universal and ancestral: without their presence, kick-starting metabolic networks is impossible, even if all enzymes and genes are present in the same cell. Identification of metabolic replicators is also important for attempts to create synthetic cells, as some of these autocatalytic molecules will presumably be needed to be added to the system as, by definition, the system cannot synthesize them without their initial presence.