Aminopeptidases from Plasmodium falciparum, Plasmodium chabaudi chabaudi and Plasmodium berghei

ABSTRACT. Using fluorogenic substrates and polyacrylamide gels we detected in cell-free extracts of Plasmodium falciparum, Plasmodium chabaudi chabaudi and Plasmodium berghei only a single aminopeptidase. A comparative study of the aminopeptidase activity in each extract revealed that the enzymes have similar specificities and kinetics, a near-neutral pH optima of 7.2 and are moderately thermophilic. Each has an apparent molecular weight of 80,000 ± 10,000, determined by high performance liquid chromatography on a calibrated SW500 column. Whilst the P. c. chabaudi and P. berghei activity co-migrate in native polyacrylamide gels, that of P. falciparum migrates more slowly. The three enzymes can be selectively inhibited by ortho -phenanthroline and are thus metallo-aminopeptidases; however, in contrast to other aminopeptidases the metal co-factor does not appear to be Zn²⁺.     

Mitochondrial NADH dehydrogenase from Plasmodium falciparum and Plasmodium berghei

The mitochondrial electron transport system is necessary for growth and survival of malarial parasites in mammalian host cells. NADH dehydrogenase of respiratory complex I was demonstrated in isolated mitochondrial organelles of the human parasite Plasmodium falciparum and the mouse parasite Plasmodium berghei by using the specific inhibitor rotenone on oxygen consumption and enzyme activity. It was partially purified by two sequential steps of fast protein liquid chromatographic techniques from n-octyl glucoside solubilization of the isolated mitochondria of both parasites. In addition, physical and kinetic properties of the malarial enzymes were compared to the host mouse liver mitochondrial respiratory complex I either as intact or as partially purified forms. The malarial enzyme required both NADH and ubiquinone for maximal catalysis. Furthermore, rotenone and plumbagin (ubiquinone analog) showed strong inhibitory effect against the purified malarial enzymes and had antimalarial activity against in vitro growth of P. falciparum. Some unique properties suggest that the enzyme could be exploited as chemotherapeutic target for drug development, and it may have physiological significance in the mitochondrial metabolism of the parasite.     

Preservation of Borrelia kansas and Plasmodium berghei

[This corrects the article on p. 224 in vol. 20.].     

Preservation of Borrelia kansas and Plasmodium berghei

Borrelia kansas and Plasmodium berghei have been stored after slow freezing in thioglycollate-glycerol medium for a 6-month period. During this time, 75% or more of the Borrelia remained motile, many intracellular malarial parasites exhibited amoeboid movement, and the growth pattern of both organisms in mice remained unchanged.     

The Mitochondria of Pre-Erythrocytic Plasmodium berghei

Considerable sectioning was required to demonstrate the mitochondrial cristae of pre-erythrocytic Plasmodium berghei in rat liver. The cristae vary from thin, budding tubules to dilated cisternae and most are obliquely and tangentially sectioned. These factors give the impression of an unusually small number of cristae. Numerous variations of fixation protocols failed to alter significantly the appearance of pre-erythrocytic parasite membranes. The data confirm previous suppositions that certain cytoplasmic bodies noted in pre-erythrocytic mammalian malarial parasites are indeed mitochondria. The term “acristate mitochondria” should be used with great caution in that it raises a serious semantic problem.     

Plasmodium berghei: oxidant defense system

Glutathione oxidant defense system protects the erythrocyte from oxidative damage. This defense system was studied in mouse erythrocytes infected with Plasmodium berghei and in isolated parasites. The efficiency of this system was found to be increased in parasitized erythrocytes compared to the normal erythrocytes. The increase in the components of the oxidant defense system in the parasitized cells could result from parasitic addition to these components. This defense system present in the parasite may protect the parasite from oxidative damage and help the parasite in its growth and development.