J. Biol. Chem., Vol. 262, Issue 11, 4994-4999, 04, 1987

The biosynthesis of tabtoxinine-beta-lactam. Use of specifically 13C- labeled glucose and 13C NMR spectroscopy to identify its biosynthetic precursors

CJ Unkefer, RE London, RD Durbin, TF Uchytil and PJ Langston-Unkefer

Tabtoxinine-beta-lactam, an irreversible inhibitor of glutamine synthetase is produced by several pathovars of Pseudomonas syringae. We have examined tabtoxinine-beta-lactam biosynthesis, an important and poorly characterized step in pathogenesis caused by this organism. We have identified the biosynthetic precursors of tabtoxinine-beta-lactam by incorporating 13C from specifically 13C-labeled D-glucose precursors and determining the labeling pattern using 13C NMR spectroscopy. Tabtoxinine-beta-lactam is generated by combining a 4-carbon fragment, a 2-carbon fragment, and a single carbon. The 4-carbon fragment arises from aspartic acid, and the 2-carbon unit is donated from carbons 2 and 3 of pyruvate. The 6-carbon backbone of tabtoxinine-beta-lactam arises from the condensation of fragments from aspartate and pyruvate, probably using reactions analogous to the initial steps in the pathway of lysine biosynthesis.
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