Where Is Threonine Produced?

Biosynthesis. As an essential amino acid, threonine is not synthesized in humans, and needs to be present in proteins in the diet. Adult humans require about 20 mg/kg body weight/day. In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine.

How is threonine made?

Threonine is derived in two steps from homoserine (Figure 5, top line). Homoserine is phosphorylated, and threonine synthase catalyzes a complex reaction that converts the resulting homoserine phosphate to threonine. Aspartokinase-homoserine dehydrogenase I is the major homoserine dehydrogenase activity.

How is threonine synthesized in other organisms?

In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine. Homoserine undergoes O-phosphorylation; this phosphate ester undergoes hydrolysis concomitant with relocation of the OH group (Lehninger 2000).