To validate this further, we conducted stable isotope labeling experiments, including deuterated and fluorinated experiments . In the deuterated experiment, 1,1-2 H 2 -GGPP was synthesized and incubated with MicA (Methods and Supplementary Figure ). The deuterated enzymatic product was then isolated, purified, and characterized using GC-MS and NMR. The analysis revealed that the M + peak at m/z of 274.3 exhibited m/z values two Da higher than the unlabeled 1 (M + peak at m/z of 272.2) (Supplementary Figure ). The 1 H NMR spectrum of 2 H2-1 was quite similar to that of 1, except for the absence of signals for H-1 (δ H 2.12) and H-14 (δ H 1.21). Moreover, H-2 of 2 H2-1 displays a singlet, and H-13 exhibits a triplet of doublets splitting pattern rather than a respective doublet and a quartet of doublets pattern in 1 (Fig. and Extended Data Figs. ). The corresponding carbon signals of C-1 and C-14 also show a consistently decreased triplet resulting from deuterium isotope effects (Fig. ) . Additionally, a comparison of HSQC spectra of 1 and 2 H 2 -1 together with 2 H NMR spectral analysis of 2 H2-1 (Supplementary Figure ) apparently targeted the deuterated carbons: C-1 and C-14 (Fig. , Supplementary Figures and).