Analysis of Conformationally Restricted α-Ketoglutarate Analogues as Substrates of Dehydrogenases and Aminotransferases

Abstract

Five synthetic, conformationally restricted α-ketoglutarate analogues were tested as substrates of a variety of dehydrogenases and aminotransferases. The compounds were found not to be detectable substrates of glutamate dehydrogenase, l-leucine dehydrogenase, l-phenylalanine dehydrogenase, lactate dehydrogenase, malate dehydrogenase, glutamine transaminase K, aspartate aminotransferase, alanine aminotransferase, and α-ketoglutarate dehydrogenase complex. However, two thermostable aminotransferases were identified that catalyze transamination between several l-amino acids (e.g., phenylalanine, glutamate) and the α-ketoglutarate analogues of interest. Transamination between l-glutamate (or l-phenylalanine) and the α-ketoglutarate analogues was found to be 0.13 to 1.08 μmol/h/mg at 45°C. The products resulting from transamination between l-phenylalanine and the α-ketoglutarate analogues were separated by reverse-phase HPLC, and the newly formed amino acid analogues were analyzed by LC-MS in an ion selective mode. In each case, the ions obtained were consistent with the expected product and a representative example is provided. The possibility existed that although the α-ketoglutarate analogues are not substrates of the dehydrogenases and most of the aminotransferases investigated, they might be good inhibitors. Weak inhibition of aminotransferases and glutamate dehydrogenase was found with some of the α-ketoglutarate analogues. The newly available thermostable aminotransferases may have general utility in the synthesis of bulky l-amino acids from the corresponding α-keto acids.