Comparison of the distribution of amino acid biosynthetic costs among the three domains. The amino acid biosynthetic cost was as reported by Seligmann . Briefly, the molecular weight was used as a proxy for biosynthetic cost, which has the advantage in comparisons across species of being independent of the pathways for amino acid synthesis [46,47]. The cost in each species was taken as the accumulation of the costs of the 20 amino acid costs (amino acid percentage multiplied its molecular weight).
Chen et al. BMC Evolutionary Biology 2013 13:219 doi:10.1186/1471-2148-13-219