8.7.3. Theorell-Chance Sequential mechanism
It is a type of ordered sequential bisubstrate reaction in which the ternary complex does not accumulate.
8.7.4. Ping pong mechanism
The other possibility in bi-substrate reaction is that one substrate, A, binds to the enzyme and on reacting with it a product, P, is released and enzyme turns into a modified form, E′. The second substrate, B, comes in and binds with modified enzyme to yield second product, Q and regenerate the enzyme, E.
The reactions following the above mechanism are called Ping-Pong or double-displacement reactions. This type of mechanism is observed in reactions catalyzed by aminotransferases.
These enzymes catalyze the transfer of an amino group from an amino acid to an α-keto acid.The products formed are a new amino acid corresponding to keto acid and a new keto acid corresponding to carbon skeleton of amino acid such as:-
Another example of ping pong reaction is phosphoglycerate mutase. The enzyme get phosphate from one substrate and after phosphorylation of enzyme, the phosphate is transferred to second substrate.