The phospholipases of Trypanosoma brucei bloodstream forms and cultured procyclics

Phospholipase from Trypanosoma brucei bloodstream forms was characterized and subsequently localized. The enzyme had a specific activity of 100 nmol . min-1 . mg-1 protein. The major portion (greater than 90%) was a soluble phospholipase A1 with a pH optimum around 6; the remainder, also phospholipase A1, was particle-bound and had an optimal activity around pH 5.2. Both enzymes were maximally activated by 0.2% Triton X-100 but differed in their sensitivity towards the inhibitory action of higher concentrations of this detergent and diisopropyl fluorophosphate, the particle-bound activity being more sensitive than the soluble one. Cell fractionation showed that the particle-bound, more acidic phospholipase A1 was associated with alpha-mannosidase- and acid proteinase-containing lysosomes. Cultured procyclic trypomastigotes also contained phospholipase A but its specific activity was only 15% of that of bloodstream forms. This drastic reduction in overall activity upon transformation from bloodstream to culture form was the result of a decrease in soluble phospholipase, whereas the lysosomal activity essentially remained unchanged.