Catabolism of Pipecolate to Glutamate in Pseudomonas putida

In the presence of pipecolate, Pseudomonas putida P2 (ATCC 25571) converts α-amino[6-14C]adipate to radioactive glutamate with a 14C distribution of 11% and 80% in carbons 1 and 5, respectively. This labeling pattern, when considered with previous data, indicates that α-aminoadipate is an obligate intermediate in the metabolism of pipecolate to glutamate. Some of the 14C in carbon 1 results from tricarboxylic acid cycle activity since cells incubated in the presence of malonate form glutamate with only 5.6% 14C in carbon 1. Cells incubated with dl-[2-14C]pipecolate form [1-14C]glutamate, which distinguishes between two possible pathways for pipecolate catabolism. While this data excludes glutarate as an intermediate in the metabolism of pipecolate to glutamate, dl-α-amino[6-14C]adipate forms radioactive glutarate and [1,5-14C]glutarate forms [1,5-14C]glutamate. From these results and earlier studies it is concluded that the major pathway for l-pipecolate catabolism in P. putida P2 is different from that in mammals. A proposed pathway includes enzyme-bound, or derivatives of, glutarate, glutaconate, and α-hydroxyglutarate as intermediates. The pathway for formation of radioactive glutarate from dl-α-amino[6-14C]adipate is unknown but could represent a minor contribution by a second catabolic pathway. Radioactive glutamate formed from [1,5-14C]glutarate containing 14C in carbon 1 is evidence for a glutarate catabolic route different from that inferred for Pseudomonas fluorescens and mammalian tissue.