Quantification of Coral Prenylquinones

Coral nubbins for prenylquinone extraction were stored in liquid nitrogen for a maximum of 48 hours. Nubbins were extracted using a 1:1 mixture of isopropanol and ethyl acetate containing 0.1 μM CoQ₉ (internal standard). Coral CoQ₁₀ and Symbiodinium PQ₉ pools were quantified by LC-MS using a slightly modified method of Lutz et al. [25 (link)]. In brief: prenylquinones were resolved using a Phenomenex Kinetex C18 column (150 mm × 4.6 mm, 2.6 μm particle size) on an Agilent 1100 series HPLC (Agilent, USA) coupled to a Bruker Esquire 3000 (Bruker Daltonics, USA). Absolute quantities of the prenylquinones were calculated from calibration plots obtained from standard compounds containing 0.1 μM CoQ₉ (internal standard). CoQ and PQ redox states (%PQH₂ and %CoQH₂) were expressed as the proportion of reduced to total (oxidised + reduced) prenylquinone. Coral CoQ data could potentially be biased by CoQ of Symbiodinium; however, symbiont CoQ was not detected with the method applied here, either because Symbiodinium type C2 contains a different isoform than the host CoQ₁₀ or because concentrations are below the detection limit [37 (link)].