Aromatic Amino Acid Transamination and Methionine Recycling in Trypanosomatids

• Published in: Proceedings of the National Academy of Sciences - PNAS 1996-04, Vol.93 (9), p.4126-4130
• Main Authors: Berger, Bradley J., Dai, Wei Wei, Wang, Hsin, Stark, Ruth E., Cerami, Anthony
• Format: Article
• Language: English
• Subjects: Amino acid metabolism; Amino acids; Amino Acids - metabolism; Animals; Biology; Crithidia fasciculata; Crithidia fasciculata - metabolism; Cyclic amino acids; Enzyme preparations; Enzymes; Indoles; Isotope Labeling; Liver; Male; Methionine - metabolism; Nitrogen Isotopes; Parasites; Phosphates; Rats; Rats, Sprague-Dawley; Recycling; Subcellular Fractions - metabolism; Trypanosoma brucei; Trypanosoma brucei brucei - metabolism; Tyrosine - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.9.4126

Although trypanosomatids are known to rapidly transaminate exogenous aromatic amino acids in vitro and in vivo, the physiological significance of this reaction is not understood. In postmitochondrial supernatants prepared from Trypanosoma brucei brucei and Crithidia fasciculata, we have found that aromatic amino acids were the preferred amino donors for the transamination of α -ketomethiobutyrate to methionine. Intact C. fasciculata grown in the presence of [15N]tyrosine were found to contain detectable [15N]methionine, demonstrating that this reaction occurs in situ in viable cells. This process is the final step in the recycling of methionine from methylthioadenosine, a product of decarboxylated S-adenosylmethionine from the polyamine synthetic pathway. Mammalian liver, in contrast, preferentially used glutamine for this reaction and utilized a narrower range of amino donors than seen with the trypanosomatids. Studies with methylthioadenosine showed that this compound was readily converted to methionine, demonstrating a fully functional methionine-recycling pathway in trypanosomatids.