title: Early evolution of efficient enzymes and genome organization.
abstract: BACKGROUND
  Cellular life with complex metabolism probably evolved during the reign of RNA, when it served as both information carrier and enzyme. Jensen proposed that enzymes of primordial cells possessed broad specificities: they were generalist. When and under what conditions could primordial metabolism run by generalist enzymes evolve to contemporary-type metabolism run by specific enzymes?
  
  
  RESULTS
  Here we show by numerical simulation of an enzyme-catalyzed reaction chain that specialist enzymes spread after the invention of the chromosome because protocells harbouring unlinked genes maintain largely non-specific enzymes to reduce their assortment load. When genes are linked on chromosomes, high enzyme specificity evolves because it increases biomass production, also by reducing taxation by side reactions.
  
  
  CONCLUSIONS
  The constitution of the genetic system has a profound influence on the limits of metabolic efficiency. The major evolutionary transition to chromosomes is thus proven to be a prerequisite for a complex metabolism. Furthermore, the appearance of specific enzymes opens the door for the evolution of their regulation.
  
  
  METHODS
  This article was reviewed by Sándor Pongor, Gáspár Jékely, and Rob Knight.
authors.affiliation: Department of Plant Taxonomy and Ecology, Institute of Biology, Eötvös University, Pázmány Péter sétány 1/C, 1117, Budapest, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Szilágyi
authors.forename: Adám
authors.initials: A
authors.lastname: Kun
authors.forename: Eörs
authors.initials: E
authors.lastname: Szathmáry
mesh_terms: D002384:Catalysis; D002875:Chromosomes; D019295:Computational Biology; D004798:Enzymes / Q000235:genetics* / Q000378:metabolism*; D019143:Evolution, Molecular; D016678:Genome; D053858:Metabolic Networks and Pathways; D008957:Models, Genetic; D016337:RNA, Catalytic / Q000235:genetics*; D012641:Selection, Genetic; D013379:Substrate Specificity
chemical_list: D004798:Enzymes; D016337:RNA, Catalytic