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The kinetic properties of Trypanosoma brucei brucei triose-phosphate isomerase are compared with those of the commercially available rabbit muscle and yeast enzymes and with published data on the chicken muscle enzyme. With glyceraldehyde 3-phosphate as substrate Km= 0.25 ± 0.05 mM and kcat= 3.7 × 105 min−1. With dihydroxyacetone phosphate as substrate Km= 1.2 ± 0.1 mM and kcat= 6.5 × 104 min−1. The pH dependence of Km and Vmax at 0.1 M ionic strength is in agreement with the results published for the yeast and chicken muscle enzymes. At ionic strength below 0.05 M the effect of a charged group specific for the trypanosomal enzyme and absent from the yeast and rabbit muscle enzymes becomes detectable. This effect significantly increases Km whereas Vmax becomes slightly higher. Trypanosomal triose-phosphate isomerase is inhibited by sulphate, phosphate and arsenate ions, by 2-phosphoglycolate and a number of documented inhibitors in the same concentration range as are the other triose-phosphate isomerases. The trypanocidal drug, Suramin inhibits T. brucei and rabbit muscle triose-phosphate isomerase to the same extent while leaving the yeast enzyme relatively unaffected.