Conventional notation in biochemical thermodynamics

In this book, we follow the convention that the term species refers to a unique chemical compound, while a reactant is a biochemical compound that may be present as a number of related and rapidly inter-converting species. In a modern biochemistry textbook a reaction, such as the ATP hydrolysis reaction 

1 The reactant inorganic phosphate is sometimes abbreviated P . Because in later chapters we use subscripts to indicate compartment, we stick to the convention here of abbreviating reactants using all capital letters. 

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