* threonine → isoleucine
* Isoleucine is an **essential amino acid**, meaning it is not synthesised by the body in humans (and hence must be ingested)
* **Food sources rich in isoleucine** include eggs, seaweed, fish, cheese, chicken and lamb
* In plants and bacteria, isoleucine may be synthesised from threonine in a five-step reaction pathway
* In the first step of this process, threonine is converted into an intermediate compound by an enzyme (threonine deaminase)
* Isoleucine can bind to an allosteric site on this enzyme and function as a non-competitive inhibitor