MALARIA PARASITES - ENZYMES INVOLVED IN RED-BLOOD-CELL INVASION

Three enzymes have been described in malaria merozoites: a serine-prot ease and two phospholipases. The parasite serine-protease is necessary for parasite entry into the red blood cell. This enzyme is synthesize d by intraerythrocytic schizonts as a glycolipid-anchored membrane pre cursor, harbouring a preformed serine-protease active site but no dete ctable proteolytic activity. Detection of the enzymatic activity corre lates with the solubilisation of the enzyme by a parasite glycolipid-s pecific phospholipase C in merozoites. A third enzyme has been detecte d with glycolipid-degrading activity, presumably a lipase A. These act ivities participate in a biochemical cascade originating with the atta chment of the merozoite to the red blood cell, including the transloca tion of the phospholipase C to the membrane-bound protease, the solubi lisation/activation of the protease and its secretion at the erythrocy te/parasite junction and ending with the entry of the parasite into th e host cell. Both the phospholipase C and the lipase A might generate secondary messages in the merozoite. Our current knowledge concerning these enzymes is presented.