Metabolism of putrescine to 5-hydroxy-2-pyrrolidone via 2-pyrrolidone.

Incubation of 2-[14C]pyrrolidone with sliced rat liver and analysis of the incubation medium by silica gel chromatography revealed that 2-[14C]pyrrolidone is metabolized to an unknown. It was previously shown by Lundgren and Hankins ((Lundgren, D.W, and Hankins, J. (1978) J. Biol. Chem. 253, 7130-7133) that slices of rat liver readily synthesized 2-pyrrolidone from putrescine. The unknown metabolite was partially purified by methanol/chloroform extraction, activated charcoal column chromatography, and two-dimensional thin layer chromatography on silica gel plates. The 2-pyrrolidone metabolite was derivatized with bis(trimethylsilyl)trifluroacetamide and analyzed by gas chromatography-mass spectrometry. The mass of the molecular ion (245) and fragment ions suggests that the 2-pyrrolidone metabolite is 5-hydroxy-2-pyrrolidone. The mass spectrum of synthetic 5-hydroxy-2-pyrrolidone was identical to that of the unknown metabolite. Synthetic 5-hydroxy-2-[3H]pyrrolidone co-chromatographed on silica gel sheets with the unknown 2-[14C]pyrrolidone metabolite obtained directly from incubation media. Under appropriate conditions (pH 7.5, no acid treatment of medium), putrescine is metabolized to 5-hydroxy-2-pyrrolidone via 2-pyrrolidone. Several effector compounds, but not necessarily the same ones, inhibit or enhance, or both, the conversion of putrescine to 2-pyrrolidone and of 2-pyrrolidone to 5-hydroxy-2-pyrrolidone. This is the first demonstration of the biosynthesis of 5-hydroxy-2-pyrrolidone.