= Phosphorolysis
\b[Phosphorolysis] is cleavage of a <chemical bond> by reaction with inorganic <phosphate>, with a phosphate group becoming part of a product. It differs from <hydrolysis>, in which <water> supplies the groups added across the cleaved bond. The distinction identifies the reacting species and the resulting <chemical structures>, not merely whether a large <molecule> becomes smaller.
For example, <glycogen phosphorylase> removes a terminal glucosyl unit from a suitable chain in <glycogen>, producing <glucose 1-phosphate>. Suppressing protonation details, write
$$
G_n+P_i\rightleftharpoons G_{n-1}+\alpha\text{-D-glucose 1-phosphate},
$$
where $G_n$ denotes the glucan chain and $P_i$ inorganic <phosphate>. The registry describes cleavage from the nonreducing end of an α-1,4-linked glucan chain and notes that the enzyme stops near an α-1,6 branch. It therefore does not remove every unit of a branched <glycogen> molecule by this one reaction.<Enzyme Nomenclature by the IUBMB>[EC 2.4.1.1, Reaction and Comments; https://iubmb.qmul.ac.uk/enzyme/EC2/4/1/1.html]{ref}
As an original <stoichiometry> example, ten permitted cleavage events consume ten inorganic phosphate units and release ten <glucose 1-phosphate> molecules. No <adenosine triphosphate> is required by this written reaction. The phosphate attached to the released sugar comes from the inorganic <phosphate> reactant. Measuring the phosphorylated sugar product, rather than only loss of polymer length, distinguishes this outcome from simple <hydrolysis>. Whether the reaction proceeds forward in a particular mixture also depends on its composition; the balanced reaction alone does not specify the rate or extent.
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