Sentence:  Carotenoid <WSD>cleavage</WSD> oxygenases (CCOs) are a class of enzymes that oxidatively cleave carotenoids into apocarotenoids. Carotenoid <WSD>cleavage</WSD> oxygenases have been identified in plants and animals and produce a wide range of <WSD>cleavage</WSD> products. ... Two of the three enzymes showed <WSD>cleavage</WSD> of β, β-carotene at the 9,10 and 15,15' position, respectively. 
Meaning of the word marked with <WSD> tags:  The splitting of a large molecule into smaller ones.