The DNA polymerases ofLeishmania mexicana

Partial purification and characterization of mitochondrial DNA polymerase from Plasmodium falciparum

Mitochondria of chloroquine-resistant Plasmodium falciparum (K1 strain) were isolated from mature trophozoites by differential centrifugation. The mitochondrial marker enzyme cytochrome c reductase was employed to monitor the steps of mitochondria isolation. Partial purification of DNA polymerase from P. falciparum mitochondria was performed using fast protein liquid chromatography (FPLC). DNA polymerase of P. falciparum mitochondria was characterized as a gamma-like DNA polymerase based on its sensitivity to the inhibitors aphidicolin, N-ethylmaleimide and 9-beta-D-arabinofuranosyladenine-5'-triphosphate. In contrast, the enzyme was found to be strongly resistant to 2',3'-dideoxythymidine-5'-triphosphate (IC(50)>400 microM) and differed in this aspect from the human homologue, possibly indicating structural differences between human and P. falciparum DNA polymerase gamma. In addition, the DNA polymerase of parasite mitochondria was shown to be resistant (IC(50)>1 mM) to the nucleotide analogue (S)-1-[3-hydroxy-2-phosphonylmethoxypropyl]adenine diphosphate (HPMPApp).

Isolation and partial characterization of three DNA polymerases from Trypanosoma cruzi

Three distinct DNA polymerase fractions (A, B and C), were isolated from Trypanosoma cruzi epimastigote forms. Fraction A is a low molecular mass enzyme corresponding to beta-like DNA polymerase of T. cruzi. Fraction B co-purified along several purification steps with fraction A, but in the last step it was clearly separated by a phosphocellulose chromatography. Fraction C was separated from fractions A and B by binding to DEAE-cellulose column, since the other two fractions were eluted in the flowthrough. This enzyme has an apparent native molecular mass of 100 kDa and showed a high preference for poly(dC)-oligo(dG) among different template-primers tested as substrate. Western-blot and biochemical analysis strongly suggest that the three DNA polymerase fractions correspond to different molecular entities. These results are in agreement with the idea that fraction C is a new DNA polymerase of T. cruzi, not described before.

Detection and characterization of DNA polymerase activity in Entamoeba histolytica

DNA polymerase activity was detected and characterized in nuclear extracts from trophozoites of Entamoeba histolytica. The activity was high at pH 2 to pH 6, but at pH 8 and 10 the activity was very low. The presence of K+ was inhibitory for the activity and a higher concentration of K+ markedly inhibited the activity. Magnesium ions (Mg2+) were absolutely required for activity and its optimal concentration was 6 to 8 mM. The activity was markedly inhibited by aphidicolin which is an inhibitor of mammalian DNA polymerases alpha, delta, and epsilon and also by N-ethylmaleimide which is an inhibitor of DNA polymerases, alpha, gamma, delta and epsilon. However, inhibition of the activity by 2', 3'-dideoxythymidine-5'-triphosphate which is an inhibitor of DNA polymerases beta and gamma was relatively weak. Thus sensitivity of the E. histolytica enzyme to these inhibitors was similar to that of mammalian DNA polymerases (alpha, delta and epsilon) of the alpha family. Monoclonal antibodies against human DNA polymerase alpha did not bind to DNA polymerase of E. histolytica.

Detection and characterization of DNA polymerase activity in Toxoplasma gondii

A DNA polymerase activity has been detected and characterized in crude extracts from tachyzoites of Toxoplasma gondii. The enzyme has a sedimentation coefficient of 6.4 S, corresponding to an approximate molecular weight of 150,000 assuming a globular shape. Like mammalian DNA polymerase alpha, the DNA polymerase of T. gondii was sensitive to N-ethylmaleimide and inhibited by high ionic strength. However, the enzyme activity was not inhibited by aphidicolin which is an inhibitor of mammalian DNA polymerases alpha, delta and epsilon and also cytosine-beta-D-arabinofuranoside-5'-triphosphate which is an inhibitor of alpha polymerase. The activity was inhibited by 2',3'-dideoxythymidine-5'-triphosphate which is an inhibitor of mammalian DNA polymerase beta and gamma. Magnesium ions (Mg2+) were absolutely required for activity and its optimal concentration was 6 mM. The optimum potassium (K+) concentration was 50 mM and a higher concentration of K+ markedly inhibited the activity. Activity was optimal at pH 8. Monoclonal antibodies against human DNA polymerase alpha did not bind to DNA polymerase of T. gondii. Thus the T. gondii enzyme differs from the human enzymes and may be a useful target for the design of toxoplasmacidal drugs.