Metabolism of tyrosine and phenylalanine in Trtpanosoma brucei gambiense

Abstract

1. 1. Soluble extracts of Trypanosoma brucei gambiense were found to contain high activity of the enzyme l-tyrosine: α-ketoglutarate aminotransferase (EC 2.6.1.5) amounting to 1.69 μmoles of tyrosine transaminated/mg. of protein/hour. 2. 2. Living, sonicated and sonicated + dialyzed preparations of this protozoan metabolized [ 14C] tyrosine to p-hydroxyphenylpyruvate and p-hydroxyphenyIlactate and [ 14C] phenylalanine to phenylpyruvate. Hydroxylation of tyrosine to 3,4-dihydroxyphenyIalanine (DOPA) and of phenylalanine to tyrosine, was not detected. 3. 3. Transamination of tyrosine by dialyzed enzyme preparations required both α-ketoglutarate and pyridoxal phosphate, while transamination of phenylalanine required only α-ketoglutarate. Two different transaminases appear to be responsible for the transamination of these two amino acids. 4. 4. Synthesis of p-hydroxyphenyllactate from [ 14C] tyrosine required NADH. 5. 5. Noradrenaline, DOPA and α-methyl p-tyrosine all inhibited the tyrosine aminotransferase to differing extents.