FIG 6 .

[¹⁵N]HMP was isolated from E. coli cells grown in the presence of [¹⁵N]threonine. (A) The IlvA- and TrpD-dependent mechanism of PRA synthesis is incorporated in the purine-thiamine (HMP) biosynthetic pathway. Nitrogen atoms are color coded based on their origin (12, 37, 38). The nitrogen derived from PRA (via PurF or TrpD or nonenzymatically) is blue, the glycine-derived nitrogen (PurD reaction) is pink, and the nitrogen derived from glutamine via PurL is green. (B and C) Mass spectral data from +TOF MS analysis of ETMP isolated from DM14893 (thrC purK) grown in the glucose-plus-adenine minimal medium containing [¹⁴N]threonine (B) or [¹⁵N]threonine (C) are shown. The expected m/z of unlabeled ETMP in this mode is 184.2819, and [¹⁵N]ETMP with one or two heavy nitrogens should be +1 or +2 atomic mass units (amu), respectively.