Isolation and characterization of the plasma membrane of human erythrocytes infected with the malarial parasite Plasmodium falciparum.

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Abstract
Human erythrocytes infected with the malarial parasite P. falciparum were labeled metabolically with a mixture of 15 radioactive amino acids. When synchronously growing parasites were at the schizont stage of development, infected cells were concentrated and purified by using a Percoll-Hypaque gradient. The plasma membrane of the infected erythrocyte, isolated by binding cells to a solid support (Affi-Gel 731, Bio-Rad), was < 1% contaminated with parasite membranes. Erythrocyte membrane proteins were analyzed by polyacrylamide gel electrophoresis and autoradiography. Despite the high sensitivity of the procedure, there was no evidence for the insertion of parasite proteins into the infected host cell membrane. One possible exception is a Mr [molecular ratio] 230,000 parasite protein present maximally as 9000 copies/infected erythrocyte membrane. No differences in the membrane proteins were observed between a highly knobby clone and a knobless clone of the same strain of P. falciparum. Apparently, parasite protein(s) do not play a structural role in the formation of knobs on the erythrocyte surface. Whether the antigenic determinants on the P. falciparum-infected erythrocyte are of parasite origin or represent newly exposed or chemically modified erythrocyte determinants was questioned.