Malarial pigment-dependent error in the estimation of hemoglobin content in Plasmodium falciparum-infected red cells: implications for metabolic and biochemical studies of the erythrocytic phases of malaria.

Measurements of mean corpuscular hemoglobin (MCH) in Plasmodium falciparum-infected red cells cultured in vitro revealed that malarial pigment (hemozoin) interferes with a true estimate of the actual hemoglobin content in Drabkin's reagent. When the hemozoin pigment was removed by passage of the lysate over a Biorex 70 column, a lower MCH value was obtained which allowed one to estimate that, under these conditions, the parasite consumes about 25% of the red cell's initial hemoglobin. Because spectrophotometric examinations of infected red cell lysates in Drabkin's reagent detect the unchanging heme content of infected red cells (hemoglobin + hemozoin), it can be used for expressing enzymatic activity or metabolite content. Results agree with simultaneous measurements on a per cell basis. However, it is suggested that instead of per gram hemoglobin, the activity should be stated as per mmole (or mumole) heme pigment. The ability to estimate accurately the consumption of intracellular hemoglobin will be useful in metabolic and pharmacologic studies of the parasite/red cell interaction.