Associate Professor of Chemistry Kenyon College Gambier, Ohio
Body of Abstract: In plants, the non-proteinogenic amino acid, β-alanine, serves as a key intermediate in the synthesis of the essential molecules vitamin B5 and coenzyme A (CoA). The production of vitamin B5 via the condensation of pantoate and β-alanine is highly conserved among plants and bacteria. The synthesis of the former (pantoate) from valine is similarly conserved among plants and bacteria while that of the latter (β-alanine) is not. Previous studies in plants found that polyamines, uracil, and propionate can all serve as intermediates in pathways leading to β-alanine. The catabolic pathways of the branched-chain amino acids (BCAAs) valine and isoleucine result in the production of propionyl-CoA (a derivative of propionate), which, in plants, is typically converted to acetyl-CoA via beta-oxidation. However, one of the intermediates of propionyl-CoA degradation, malonate semialdehyde, can react to form β-alanine via transamination. Therefore, we hypothesized that BCAAs could also serve as a source of β-alanine. To trace the production of β-alanine from propionyl-CoA and isoleucine, we treated wild-type and transgenic seedlings with isotopically-labeled precursors and analyzed extracts using 13C-NMR and GC-MS. We observed the production of both β-alanine and a key intermediate, 3-hydroxypropionate, in samples treated with propionate and isoleucine. Additionally, we identified three aminotransferases from A. thaliana that catalyzed the reversible transamination reaction. These results affirm our hypothesis that isoleucine, and possibly valine, can serve as a precursor in the synthesis of β-alanine via propionyl-CoA metabolism and transamination of metabolic intermediates.