The Biological System of the Elements (BSE). Part II: a theoretical model for establishing the essentiality of chemical elements. The application of stoichiometric network analysis to the biological system of the elements

Stoichiometric Network Analysis (SNA), originally developed by the Canadian chemist Bruce L. Clarke during the 1970s, provides a most efficient means of reducing the background topology of complex interaction networks to some skeleton topology around which systems dynamics can be understood without jeopardising insight into complex dynamics by over- or miss-simplification, Since it focuses on the corresponding autocatalytic (AC) features of a fee dback system as those which control overall behaviour to some extent, SNA d eals with reaction kinetics in and beyond chemistry, e.g, with nuclear reac tions. It is therefore quite straightforward to apply this manner of simpli fication, which in turn is supported by a number of mathematical theorems o n systems behaviour and properties of AC cycles, to biological systems alth ough their 'full' complexity may not even be assessed in the yet rare cases of complete genetic sequencing. Assuming there is a relationship between t he kinds of metal or metalloid species and key biological/biochemical trans formations to be promoted with their aid - this relationship being the subj ect of bio-inorganic chemistry - and that biochemistry is, in effect, about systems which can reproduce and thus behave autocatalytically, one can exp ect SNA to yield formally sound statements on basic features of biology and biochemistry too. if we sum up the facts and considerations concerning ess entiality or possible essentiality in a biological system of elements (Mark ert, 1993), this means joining the triangular representation of BSE, includ ing statements on (the degree of biological) evolution and aggregation leve ls, to SNA treatment of autocatalysis within hierarchical systems from meta lloenzymes to entire biocoenoses. Arguments using preferred cluster sizes a nd aggregation tendencies from coordination chemistry are then employed to circumscribe possible functions within the BSE. They are also extended to m etals hitherto not known to be essential, such as tellurium or scandium. (C ) 2000 Elsevier Science B.V. All rights reserved.