In enzymology, a prenylcysteine oxidase (EC 1.8.3.5) is an enzyme that catalyzes the chemical reaction

an S-prenyl-L-cysteine + O₂ + H₂O ${\displaystyle \rightleftharpoons }$ a prenal + L-cysteine + H₂O₂

The 3 substrates of this enzyme are S-prenyl-L-cysteine, O₂, and H₂O, whereas its 3 products are prenal, L-cysteine, and H₂O₂.

This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with oxygen as acceptor. The systematic name of this enzyme class is S-prenyl-L-cysteine:oxygen oxidoreductase. This enzyme is also called prenylcysteine lyase.

• Prenylcysteine oxidase 1, symbol PCYOX1, gene on chromosome 2

• Hemithioacetals in nature, for mechanism of action
• Flavin adenine dinucleotide, cofactor of the enzyme
• Prenylation, a process forming S-prenyl-L-cysteine