Figure 3.

Nucleotide selectivity. The indicated enzyme (50 μM) was mixed with 2 mM SAM and 1 mM deuterium-labeled CTP (deuCTP) for MmVip or NvVip, deuterium-labeled UTP (deuUTP) for TvVip and SbVip, or deuterium-labeled GTP (deuGTP) for LmVip, in addition to 1 mM of each of three remaining unlabeled nucleotides. The resulting 5′-dA is determined, and the ratio of heavy to light 5′-dA is plotted. The transfer of a deuteron to 5′-dA (deu5′-dA) will occur if the enzyme is selective for the deuterium-containing substrate. All enzymes are selective for their respective substrates and do not abortively produce 5′-dA under these conditions. N = 3.