Ultrastructural localization of enzymes involved in the feeding process in Plasmodium chabaudi and Babesia hylomysci.

In P. chabaudi, hemoglobin digestion occurs in two ways: micropinocytosis and cytostomal phagocytosis. Both mechanisms lead to the formation of digestive vesicles which evolve to pigment vesicles containing hemozoin crystals. We used ultrastructural enzyme cytochemistry to detect and localize endoarylamidase and aminopeptidase activity. In P. chabaudi, these two enzymes are at first detected at the level of cytoplasmic ribosomes. When pinocytic vesicles appear, enzyme activity is localized at the membrane of the newly formed vesicles. Then, the labelling extends to the vesicle contents where it becomes very prominent. In the late trophozoite, enzymatic activity decreases and is no longer detected. In B. hylomysci, no endoarylamidase activity can be detected. Aminopeptidase is noted in the cytoplasm, the labelling being heavier in the growing trophozoites than in the younger stages. No vesicles or pigment can be observed. We thus conclude that aminopeptidase or endoarylamidase are synthesized in the cytoplasm of P. chabaudi and migrate to the digestive vesicles where hemoglobin digestion occurs. We do not know whether Babesia degrades hemoglobin since it does not produce residual pigment. It could feed from small peptides or amino acids coming from or through the stroma of the red blood cell.