Stable crosslinks of collagen

It has recently been proposed that the syndesine crosslinks of collagen possess their unique stability because they can isomerize to a α-keto-amine. Although this type of isomerization is perfectly feasible for α-hydroxy-aldimines like syndesine, the present studies suggest that the amount of α-keto-amine present in some tissues is far too low to account for the observed stability. However, it is possible that the syndesine crosslinks adopt a cyclic hydrogen-bonded conformation. This could present considerable steric hindrance to hydration of the CN bond, rendering this aldimine crosslink much more stable than those with no α-hydroxy group.