Phosphorolysis involves the cleavage of a bond by addition across that bond of the elements of phosphoric acid. An enzyme catalyzing a phosphorolysis is called a phosphorylase, to be distinguished from a phosphatase (or, more precisely, a phosphohydrolase), which catalyzes the hydrolytic cleavage (hydrolysis) of a phosphate ester bond.

Energetically speaking, the phosphorolytic mechanism has an advantage in mobilization of glycogen, which yields most of its monosaccharide units in the form of sugar phosphates (glucose-1-phosphate). These units can be converted to glycolytic intermediates directly, without the investment of additional ATP. By contrast, starch digestion yields glucose plus some maltose. ATP and the hexokinase reaction are necessary to initiate glycolytic breakdown of these sugars.