| P5C | Δ1-Pyrroline-5-carboxylate |
| GSA | L-Glutamate γ-semialdehyde |
| ProC | Δ1-Pyrroline-5-carboxylate reductase (from E. coli, if not otherwise specified) |
| THP | L-thioproline |
| DHP | 3,4-dehydro-L-proline |
| A2C | L-azetidine-2-carboxylate |
| P6C | Δ1-piperideine-6-carboxylate |
| PIP | L-pipecolate |