Sialoglycoproteins and sialic acids ofPlasmodium knowlesischizont-infected erythrocytes and normal rhesus monkey erythrocytes

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Abstract
SUMMARY: The effects of malaria infection on RBC sialic acids and sialoglycoproteins were studied with asexual blood-stage infections ofPlasmodium knowlesiin rhesus monkeys. Glycoprotein radio-isotope labelling methods were used to compare the sialoglycoproteins of normal RBC andP. knowlesischizont-infected RBC (SI-RBC). Tritiation of glycoproteins from SI-RBC with the standard sialidase + galactose oxidase/NaB3H4method or standard periodate/NaB3H4method was significantly decreased when compared to normal RBC. However, tritium uptake into glycoproteins was normal when SI-RBC were treated with 5-fold higher concentrations of both enzymes in the first labelling method, or with a 5-fold increase in the molar ratio of periodate to sialic acid in the second method. The mobility of tritiated host cell glycoproteins on SDS–polyacrylamide gels was identical for SI-RBC and normal RBC. New bands, possibly glycoproteins, of 230, 160, 90, 52, and 30 kDa were detected after labelling SI-RBC by the modified periodate/NaB3H4method. Sialic acid analysis of normal rhesus monkey RBC (62μg/1010RBC) revealed that 46% of the total sialic acid wasN-glycolylneuraminic acid, 33% wasN-acetyl-9-O-acetylneuraminic acid, and the remainderN-acetylneuraminic acid. SI-RBC collected either directly from infected monkeys or afterin vitroculture of ring-infected RBC in horse serum, had increased total sialic acid (126 or 115μg/1010RBC, respectively). The sialic acid content of infected RBC must increase during parasite development since RBC infected with ring-stageP. knowlesihad the same content as normal RBC. There was no significant difference in the ratio of the three sialic acids of SI-RBC and normal RBC. In contrast, the uninfected RBC from infected blood of different monkeys showed marked variation in sialic acid composition and generally had a lower sialic acid content than normal RBC.