ACTIN IN THE MEROZOITE OF THE MALARIA PARASITE, PLASMODIUM-FALCIPARUM

Merozoites of the human malaria parasite, Plasmodium falciparum, when treated with cytochalasin B, will attach irreversibly to red cells wit h formation of a vestigial internal (parasitophorous) vacuole, but the y are inhibited from moving into the cell. The existence of an actin-b ased motile mechanism is implied. Immunoblotting, peptide mapping and the DNase inhibition assay have been used to show that the merozoite c ontains actin. It makes up an estimated 0.3% of the total parasite pro tein and is partitioned in the ratio of about 1:2 between the cytosoli c and particulate protein fractions. In the former it is unpolymerised and in the latter filamentous. Most of the anti-actin-reactive protei n in the soluble fraction and about 20% of that in the pellet has an a pparent molecular weight of 55,000 and reacts with an anti-ubiquitin a ntibody; it is thus evidently ubiquitinyl actin, or arthrin, which has so far been detected only in insect flight muscle.