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. 2009 Oct 29;3:103. doi: 10.1186/1752-0509-3-103

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Copyright ©2009 Pitkänen et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Reaction and metabolite junctions. Top left: atoms in metabolites m₁and m₂are transferred to atoms in metabolite m₅via two reaction paths p₁= (r₁, r₃) and p₂= (r₂, r₃) (indicated by dashed arrows). The paths merge in reaction r₃. Pathway P consisting of reactions r₁, r₂, r₃has Z_O(P, S, T) = 1, when atoms of {m₁, m₂} and {m₅} comprise the source and target sets S and T, respectively. Top right: pathway P' = {r₁, r₂, r₃} achieves Z_O(P', S, T) = 1 assuming source and target atoms to be all atoms in {m₁, m₂} and {m₄}, respectively. The two reaction paths transferring the atoms, = (r₁, r₃) and = (r₂, r₃) merge in metabolite m₃. Subsequently, atoms from m₁and m₂are never transferred to the same instance of metabolite m₃via these paths. Bottom left and right: atom graph representations of pathways P (left) and P' (right). Hollow circles denote atoms which can originate from atoms in metabolites m₁or m₂.

Inline graphic — Reaction and metabolite junctions. Top left: atoms in metabolites m₁and m₂are transferred to atoms in metabolite m₅via two reaction paths p₁= (r₁, r₃) and p₂= (r₂, r₃) (indicated by dashed arrows). The paths merge in reaction r₃. Pathway P consisting of reactions r₁, r₂, r₃has Z_O(P, S, T) = 1, when atoms of {m₁, m₂} and {m₅} comprise the source and target sets S and T, respectively. Top right: pathway P' = {r₁, r₂, r₃} achieves Z_O(P', S, T) = 1 assuming source and target atoms to be all atoms in {m₁, m₂} and {m₄}, respectively. The two reaction paths transferring the atoms, = (r₁, r₃) and = (r₂, r₃) merge in metabolite m₃. Subsequently, atoms from m₁and m₂are never transferred to the same instance of metabolite m₃via these paths. Bottom left and right: atom graph representations of pathways P (left) and P' (right). Hollow circles denote atoms which can originate from atoms in metabolites m₁or m₂.