Utilization of amino acids by Trypanosoma brucei in culture: L-threonine as a precursor for acetate.

The amino acid compositions of several culture media have been analysed and compared. The utilization and excretion of amino acids and other metabolites have been followed during growth of Trypanosoma brucei S42 in a defined medium. All of the added L-threonine was metabolized by the cells, even when it was present at elevated concentrations. Glucose was consumed throughout the growth cycle: glutamine was consumed more rapidly than glutamic acid, which was itself used at about the same rate as proline. Threonine was cleaved to form glycine and acetate, both of which accumulated in the medium. Alanine and succinate were excreted together with a small amount of pyruvate, but these three products accounted for less than half of the glucose used. CO2 production from glucose was not measured, but insignificant amounts of CO2 were produced from threonine. Tetraethylthiuram disulphide blocked the cleavage of threonine and was a potent inhibitor of trypanosome growth.