The synthesis and fate of stage-specific proteins in Plasmodium falciparum cultures.

Cultured ring, trophozoite and schizont stages of Plasmodium falciparum were metabolically labeled with [35S]methionine. After labeling, cultures were incubated for varying times in the presence of non-radioactive methionine. Triton-soluble proteins from different stages of growth were analysed by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Most proteins were synthesized by every stage of growth and remained unchanged throughout the cycle through to the ring stage following merozoite invasion of erythrocytes. At least 15 proteins, most of high molecular weight, were synthesized solely or predominantly by schizonts. Eight proteins (approx. 177, 170, 158, 87, 83, 47, 41 and 24 kDa) appeared in schizonts but not merozoites. Eight proteins (approx. 240, 203, 106, 80, 35, 19, 15 and 14 kDa) appeared in merozoites, but not in rings following merozoite invasion. Some proteins appeared to be modified after synthesis.