Abstract

The kinetic properties of aldolase from Trypanosoma brucei were studied in comparison with aldolase from rabbit muscle and Staphylococcus aureus. The 3 enzymes displayed a similar broad pH optimum for the cleavage of fructose 1,6-bisphosphate (Fru(1,6)P2) and a similar narrow pH optimum for the cleavage of fructose 1-phosphate (Fru-1-P). However, small alterations in the maximal cleavage rate at more extreme pH values yielded disparities between the pH curves. The reaction catalyzed by the aldolases from T. brucei and S. aureus proceeded via an ordered sequence, as described for the rabbit-muscle enzyme. We determined for the 3 enzymes the kinetic parameters for both the cleavage and the formation of Fru(1,6)P2 and for the cleavage of Fru-1-P. The trypanosomal enzyme differed in its higher ratio of the maximal rate of Fru(1,6)P2-cleavage vs. the maximal rate of Fru(1,6)P2-formation, its higher affinity towards dihydroxyacetone phosphate, and its higher turnover number for the cleavage of Fru-1-P. At ionic strengths above 0.1 M the kinetic parameters of the trypanosomal enzyme followed the limited form of the Debye-Hückel equation. At ionic strengths below 0.1 M the enzyme revealed a characteristic deviation: the apparent Km for Fru(1,6)P2 increased with decreasing salt concentration. The trypanosomal aldolase was competitively inhibited by adenine nucleotides and phosphates. This inhibition occurred in the same concentration range as observed for the rabbit-muscle enzyme, while the bacterial enzyme was less affected.