The assays were conducted in a 100 µL mixture containing 50 mM Tris-HCl buffer (pH 8.0), 15 mM MgCl2, 20 µM PcTS1 enzyme, and 5 mM GGPP. The reaction was initiated by adding the enzyme and incubated for 3 h at 37 °C. To quench the reaction, 200 µL of ice-cold acetonitrile and 50 µL of saturated NaCl solution were added sequentially to induce phase separation. The upper organic layer was then collected for HPLC analysis. Chromatographic separation was achieved at 35 °C and a flow rate of detailed as follows: 0-3 min at 5% CH3CN, 3-18 min ramping to 95% CH3CN, and maintaining 95% CH3CN in 18-40 min. The enzyme products were detected at 210 nm with a photodiode array detector. Similar assays were performed using 2Z-GGPP, GLPP, 1,1-D2-GGPP, or 6F-GGPP as substrates.