L-Proline
An amino acid that, once modified, forms the backbone of collagen's triple helix.
Substrate reasoning; no human skin trial of supplemental free proline.
On the label: L-Proline.
What it does for you
Part of the substrate pool collagen is assembled from.
Why we use it
Proline and its hydroxylated form are collagen-specific in a way most amino acids are not. This is where vitamin C does its work.
Mechanism
Proline is converted to hydroxyproline by an enzyme that requires vitamin C, and that conversion is what allows the collagen helix to hold its shape.