Spontaneously released merozoites from synchronous Plasmodium falciparum cultures were isolated in the presence of protease blocker. 1-5 X 10(10) merozoites were obtained in each experiment. The isolated merozoites possessed a thick surface coat and about 80% were invasive to human erythrocytes although they did not subsequently develop into ring stages. Tests using several analytical methods showed the merozoite preparations to be free of any erythrocyte contamination. Six labelled proteins were identified after surface radio-iodination, the largest with a molecular weight of 82 000. All six proteins were precipitated with various immune sera. Four other proteins with molecular weights of 200 000 and 160 000-145 000 (a triplet) were identified by precipitation with the same immune sera after metabolically labelling the merozoites. The six surface proteins were not prominent in the metabolically labelled preparations. Using these methods it is possible to identify and differentiate between surface and internal merozoite antigens.

A 46,000 dalton glycoprotein was isolated by extraction of freshly harvested P. falciparum merozoites (FCB1 strain), followed by gel electrophoresis of the extract and electroelution. The antigen is present in the late ring, trophozoite, schizont, and segmenter stages and is localized on the merozoite surface at the end of schizogony. It is not related to the 185,000-195,000 dalton schizont antigen. An antiserum against the 46,000 dalton antigen inhibits invasion of erythrocytes by merozoites. The isolated antigen is identical to the antigen against which monoclonal antibody (mcab) 13.4 is directed.

No abstract

No abstract

Using metabolic labeling techniques with either radioactive glucosamine or various sugars in synchronous Plasmodium falciparum cultures it was proven that merozoites isolated from such cultures possess glycoproteins. Biosynthesis and processing of these glycoproteins were investigated.