A mass spectrometric method to determine activities of enzymes involved in polyamine catabolism
An analytical method for the determination of three polyamines (putrescine, spermidine, and spermine) and five acetylpolyamines [N1-acetylspermidine (N1AcSpd), N8-acetylspermidine (N8AcSpd), N1-acetylspermine, N1,N8-diacetylspermidine, and N1,N12-diacetylspermine] involved in the polyamine catabolic pathway has been developed using a hybrid tandem mass spectrometer. Heptafluorobutyryl (HFB) derivatives of these compounds and respective internal standards labeled with stable isotopes were analyzed simultaneously by TOF MS, based on peak areas appearing at appropriate m/z values. The isomers, N1AcSpd and N8AcSpd were determined from their fragment ions, the acetylamidopropyl and acetylamidobutyl groups, respectively, using MS/MS with 13C2-N1AcSpd and 13C2-N8AcSpd which have the 13C2-acetyl group as an internal standard. The TOF MS method was successfully applied to measure the activity of enzymes involved in polyamine catabolic pathways, namely N1-acetylpolyamine oxidase (APAO), spermine oxidase (SMO), and spermidine/spermine N1-acetyltransferase (SSAT). The following natural substrates and products labeled with stable isotopes considering the application to biological samples were identified; for APAO, [4,9,12-15N3]-N1-acetylspermine and [1,4,8-15N3]spermidine (15N3-Spd), respectively; for SMO, [1,4,8,12-15N4]spermine and 15N3-Spd, respectively; and for SSAT, 15N3-Spd and [1,4,8-15N3]-N1-acetylspermidine, respectively. âº Compounds in polyamine catabolic pathway were determined by a column-free ESI-TOF MS. âº N1- and N8-acetylspermidine were determined by a column-free ESI-MS/MS. âº The method was applied to determine activities of APAO, SMO, and SSAT in the pathway. âº The assay method contained stable isotope-labeled natural substrates. âº It is applicable to biological samples containing natural substrate and product.