THE ANTIMALARIAL DRUG, CHLOROQUINE, INTERACTS WITH LACTATE-DEHYDROGENASE FROM PLASMODIUM-FALCIPARUM

We have previously shown that a radioiodinated photoreactive analogue of chloroquine, tylamino)quinolin-6-yl)-4-azido-2-hydroxybenzamide ([I -125]ASA-Q), specifically labels two proteins in Plasmodium falciparum with apparent molecular weights (M-r) of 42 and 33 kDa (Foley M, Dead y LW, Ng K, Cowman AF, Tilley L. J Biol Chem 1994;269:6955-6961). We n ow report the identification of the 33 kDa protein. The 33 kDa protein was purified from Plasmodium falciparum using photoaffinity labelling with [I-125]ASA-Q to monitor the enrichment process. N-terminal seque nce analysis of the purified protein revealed exact identity of the fi rst 35 amino acids with P. falciparum lactate dehydrogenase (PfLDH). T he plasmodial enzyme was cloned and expressed in E. coli and the recom binant protein used to produce a rabbit antiserum. Immunoprecipitation using affinity-purified anti-PfLDH antibodies confirmed the identity of the 33 kDa CQ-binding protein. The enzyme activity of purified PfLD H was not significantly affected by chloroquine indicating that PfLDH is not a direct target of CQ. PfLDH was, however, shown to be exquisit ely sensitive to inhibition by free heme and chloroquine protected aga inst this inhibitory effect. (C) 1997 Elsevier Science B.V.