Metabolomics in Systems Biology

The origin of metabolomics, as a part of systems biology, can be dated to the 1970s when Arthur Robinson and coworkers, in research regarding the nutritional needs of volunteers, proposed taking into account and analyzing not only one but many of the chromatographic peaks derived from metabolites in their urine [1]. 

With respect to technical differences, it should be emphasized that, for metabolomic analyses, there is no single analytical technique that allows determination of all low-molecular-weight compounds, unlike genomic and proteomic analyses. In metabolomics, various complementary analytical techniques are often used in combination with advanced bioinformatics tools for analysis of large data sets. 

The size of the metabolome varies and depends on the species and type of organism. In the case of unicellular organisms such as baker s yeast (Saccharomy-ces cerevisiae), the number of metabolites amounts to 600, which is only a tenth of the number of genes (6000). In turn, plants are characterized by a much larger number of metabolites. The metabolome of Arabidopsis Arabidopsis sp.) is estimated to be 5000 compounds. In total, the number of metabolites of all plant species is estimated at 90,000-200,000 compounds, of which secondary metabolites make up a large proportion. 

The number of human metabolites has been estimated differently by various scientists. For example, according to Kell [4], the size of the human metabolome is calculated at approximately 2700 metabolites, which are involved in 1100-3300 reactions. This is only an estimated value because the human metabolome has not been thoroughly calculated and substrates for many enzymes have not yet been discovered. Additionally, difficulties in estimation of the appropriate size of the metabolome can be attributed to the fact that many determined metabolites are exogenous in origin (derived from diet or drugs) or derived from endogenous bacterial flora. So far, the online Human Metabolome Database (http //www. hmdb.ca) contains more than 4500 metabohtes detected in human blood and 3995 metabolites detected in human urine. This database is constantly expanded and updated. It is estimated that it will eventually contain more than 10,000 metabolites. 

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Weckwerth W. Metabolomics in systems biology. Annu Rev Plant Biol 2003 54 669-689. 

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