p-quinones prenylquinone A quinone substituted by a polyprenyl-derived side-chain. Prenylquinones occur in all living cells. Due to their amphiphilic character, they are mainly located in biological membranes where they function as electron and proton carriers in the photosynthetic and respiratory electron transport chains. Some prenylquinones also perform more specialised roles sucy as antioxidants and enzyme cofactors. Prenylquinones are classified according to ring structure: the main classes are menaquinones, phylloquinones, ubiquinones and plastoquinones.