MagazineGlycine, proline, hydroxyproline: the amino acids collagen is made of
Glycine, proline, hydroxyproline: the amino acids collagen is made of
Collagen is not just a protein like any other. Its unusual composition explains why specific peptides appear in the blood from it and why it needs vitamin C.
Short answer
Collagen has a very unusual composition: roughly every third amino acid is glycine, and a lot of it is made up of proline and hydroxyproline. This trio explains a lot of things at once: why collagen is strong, why the specific peptide Pro-Hyp appears in the blood after drinking it, and why the body needs vitamin C to produce it. You will find the same three amino acids in marine collagen too.
A third is glycine
A classic analysis of fish collagens (Piez and Gross, Journal of Biological Chemistry, 1960) measured that glycine makes up around 317 to 345 residues per 1000 in the collagen of carp, cod and pike, that is roughly a third. This is no accident. Glycine is the smallest amino acid and fits inside the tightly coiled triple helix, where a larger amino acid could not squeeze through. Every third position in collagen is therefore glycine.
Proline and hydroxyproline hold the shape
Proline and hydroxyproline are imino acids with a ring structure. They act as braces that keep the triple helix from loosening. The more of them collagen has, the higher the temperature it withstands. Marine collagen has somewhat fewer of them than beef collagen, which is why it is more sensitive to heat (this is the reason for the up-to-60 °C rule).
Hydroxyproline is also a rarity. It is almost absent from ordinary dietary proteins, so when the body finds it in the blood within a peptide, it is practically a collagen signature.
Why Pro-Hyp matters
The proline-hydroxyproline bond resists digestion unusually well. That is why the Pro-Hyp pair reaches the blood intact. The study by Iwai and colleagues (Journal of Agricultural and Food Chemistry, 2005) measured it in human blood after drinking collagen as the main collagen peptide, peaking at 1 to 2 hours. Pro-Hyp also acts as a signal for fibroblasts, the cells that produce collagen. The amino acids from collagen are therefore not just bricks, but also an instruction to build.
Where vitamin C fits in
For the body to make hydroxyproline from proline and assemble collagen correctly, it needs enzymes for which vitamin C is an essential cofactor. Without vitamin C, collagen production stalls; the classic historical example is scurvy. That is why it makes sense to take collagen in the morning together with vitamin C, supplying the body with both building peptides and the cofactor for its own production at the same time.
Summary of the trio
- Glycine: every third amino acid, enables the tight triple helix.
- Proline: brace of the helix, raw material for hydroxyproline.
- Hydroxyproline: collagen's signature; in the Pro-Hyp pair it survives digestion and serves as a signal.
- Vitamin C: the cofactor without which the body does not produce hydroxyproline and collagen.
Collagen is made of amino acids that do two things at once: they build and at the same time give cells the instruction to build.
Sources
- Piez K. A., Gross J. The amino acid composition of some fish collagens. Journal of Biological Chemistry, 1960. doi.org/10.1016/S0021-9258(18)69466-9
- Iwai K. et al. Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates. Journal of Agricultural and Food Chemistry, 2005. doi.org/10.1021/jf050206p
