Covalent catalysis usually consists of a multistep reaction in which covalent bonds are formed
between the enzyme and substrate to produce reactive intermediates, followed by bond-breaking
to release the final products
For example, the transfer of a group X from molecule A to molecule B takes place in a two-step reaction:
A-X + E → A + E-X
E-X + B → E + B-X
This two-step sequence is also an important means for coupling the energy of one reaction to another.
For example, covalent catalysis of sucrose (a disaccharide of glucose and fructose) occurs through a
glucosyl-enzyme intermediate:
Sucrose + Enzyme → Glucosyl-Enzyme + Fructose
Glucosyl-Enzyme + Pi → Enzyme + Glucose-1-phosphate