Applications of deuterium labeling in the study of the in vitro conversion of delta 1-pyrroline to 4-aminobutanoic acid and 2-pyrrolidinone.

delta 1-Pyrroline is a putrescine metabolite that is biotransformed by rabbit liver preparations to 4-aminobutanoic acid and its lactam, 2-pyrrolidinone. Analysis of dilute aqueous solutions of delta 1-pyrroline by proton nuclear magnetic resonance indicated the the predominating species in the liver incubation preparations was delta 1-pyrroline monomer, although other species, such as 4-aminobutyraldehyde an delta 1-pyrroline timer, may exist in equilibrium with the monomer. [2H12]-delta 1-Pyrroline trimer was synthesized from [2H5]pyrrolidine by conversion to the N-chloro derivative followed by dehydrohalogenation. 4-Aminobutanoic acid was measured by a gas chromatographic mass spectrometric assay after derivatization with dimethylformamide dimethyl acetal. The 4-aminobutanoic acid homologue, 5-aminovaleric acid, served as internal standard. 2-Pyrrolidinone was hydrolyzed and measured as 4-aminobutanoic acid. A comparison of the amounts of product formed following incubation of labeled and unlabeled delta 1-pyrroline indicated a significant isotope effect in the formation of 2-pyrrolidinone. The influence of the label was much less on 4-aminobutanoic acid production. The results suggest that there are two separate pathways involved in the reaction.