LysylOxidase

Lysyl oxidase, commonly abbreviated LOX, is a copper-dependent amine oxidase that catalyzes the oxidative deamination of peptidyl lysine residues in collagen and elastin. This enzymatic reaction converts lysine residues into reactive aldehyde groups (allysine and hydroxyallysine), which subsequently participate in covalent cross-link formation to stabilize and stiffen the extracellular matrix (ECM). The reaction consumes oxygen and produces ammonia and hydrogen peroxide as byproducts.

The lysyl oxidase family includes LOX and the LOX-like enzymes LOXL1, LOXL2, LOXL3, and LOXL4. These proteins are generally secreted as inactive proenzymes (pro-LOX) and require proteolytic processing, by proteases such as BMP-1, to generate the active enzyme. Activation and localization are predominantly extracellular, where LOX enzymes act on collagen and elastin fibers within the ECM. Copper is a essential cofactor for catalytic activity, and the enzymes can be inhibited by copper chelators or by specific LOX inhibitors in experimental settings.

Functionally, LOX-mediated cross-linking increases the tensile strength and stability of connective tissues and contributes to basement membrane maturation and tissue remodeling. Proper LOX activity is important for development, wound healing, and normal tissue mechanics. Dysregulation of LOX or LOX-like enzymes is associated with pathological ECM remodeling, including fibrotic diseases and cancer progression, where increased cross-linking can promote tissue stiffness and metastatic potential. Clinical and research relevance is underscored by inhibitors such as beta-aminopropionitrile (BAPN) used to study LOX function and by genetic associations of LOXL1 with certain ocular conditions.