Selective interaction of glycosomal enzymes from Trypanosoma brucei with hydrophobic cyclic hexapeptides

Hydrophobic cyclic hexapeptides have been reported to selectively inhibit glycosomal triosephosphate isomerase from Trypanosoma brucei (Kuntz et al, 1992, Eur. J. Biochem., 207, 441-447). Here it is shown that this inhibition is not due to a specific interaction between the enzyme and soluble hydrophobic cyclic hexapeptides, but that it is the result of a coprecipitation of trypanosome triosephosphate isomerase with cyclic hexapeptides when the solubilities of the latter are exceeded. A study of the interaction of these hexapeptides with other glycosomal enzymes revealed that several of them, such as phosphoglycerate kinase and hexokinase, also coprecipitated with these peptides, whereas most of the homologous enzymes from other organisms did not coprecipitate, nor were they inactivated.