Fig. 2. Enzymatic versus non-enzymatic processes.

The two primary forms of crosslinks in mature tendon collagen can be identified as being driven by enzyme activity (i.e., enzymatic crosslinks) or other processes (i.e., non-enzymatic). (a) Enzymatic crosslinks are primarily mediated by LOX, which catalyzes the conversion of lysine residues (NH₂) into reactive aldehyde species (-H) and yield immature or mature divalent and trivalent crosslinks. (b) The dominant non-enzymatic crosslinks are AGEs, which are formed through glycation of protein residues, such as lysine (NH₂), by reducing sugars, such as glucose (glc). Modified with permission from Hudson et al. (2018).