Figure 1.

Central and eccentric cleavages of β-carotene. Oxidative cleavage of β-carotene at the 15, 15’ double bond is catalyzed by the enzyme β-carotene 15, 15’-oxygenase 1 (BCO1) and leads to the generation of two molecules of retinal (β-apo-15-carotenal). The cleavage at the 9’, 10’ double bond is catalyzed by β-carotene 9’,10’-oxygenase 2 (BCO2) and leads to the formation of β-apo-10’-carotenal and β-ionone. Cleavage at other double bonds can occur non-enzymatically but may also be enzymatic, as noted by the question marks in blue.