“The idea that life depends on the organization of the thousands of biochemical reactions that constitute metabolism was obvious [...]. The essential but often over-looked point is that enzymes, and all other proteins, are themselves products of metabolism, and thus metabolites”. The circular organization of living organisms was captured by Mettrie’s methaphor of ‘‘machine which winds its own springs’’
Juan-Carlos Letelier, Marıa Luz Cardenas, Athel Cornish-Bowden. From L’Homme Machine to metabolic closure. J Theor Biol. 2011.