Proline is a non-essential amino acid synthesized from glutamic acid in 3 enzyme catalyzed steps. Glutamate is phosphorilated on the gamma carbonyl to yield glutamyl phosphate by gamma-glutamyl to kinase. The glutamyl phosphate is reduced to glutamyl semialdehyde by gamma-glutamyl phosphate reductase. This spontaneously cyclizes to form pyrroline carboxylate, which is reduced to proline in the final step of synthesis by pyrroline 5-carboxylate reductase. Proline can also be synthesized from arginine in S. aureus via ornithine, which has the same carbon backbone as glutamyl semialdehyde with an amino group replacing the aldehyde.(2)
