| Definition: A conversion interaction in which one or more entities (substrates) undergo covalent changes to become one or more other entities (products). The substrates of biochemical reactions are defined in terms of sums of species. This is convention in biochemistry, and, in principle, all of the EC reactions should be biochemical reactions.
Examples: ATP + H2O = ADP + Pi
Comment: In the example reaction above, ATP is considered to be an equilibrium mixture of several species, namely ATP4-, HATP3-, H2ATP2-, MgATP2-, MgHATP-, and Mg2ATP. Additional species may also need to be considered if other ions (e.g. Ca2+) that bind ATP are present. Similar considerations apply to ADP and to inorganic phosphate (Pi). When writing biochemical reactions, it is important not to attach charges to the biochemical reactants and not to include ions such as H+ and Mg2+ in the equation. The reaction is written in the direction specified by the EC nomenclature system, if applicable, regardless of the physiological direction(s) in which the reaction proceeds. Polymerization reactions involving large polymers whose structure is not explicitly captured should generally be represented as unbalanced reactions in which the monomer is consumed but the polymer remains unchanged, e.g. glycogen + glucose = glycogen. |