Pyridoxal kinase activity in plasmodium falciparum and plasmodium berghei in vitro

Abstract

Pyridoxal kinase (PLK: EC2.7.1.35) is an essential enzyme for cellular synthesis of proteins where it plays a central role in transamination reactions. PLK is required for biosynthesis of B-6 coenzyme in which it phosphorylates pyridoxal, pyridoxine, pyridoxamine (vitamine-B6 vitamers) into their active coenzyme pyridoxal phosphate (PLP).

Intraerythrocytic parasites such as Plasmodia are known to be dependent on their hosts for biochemical products, which they are unable to synthesis but are required to sustain life. P.falciparum may lack PLK activity and may be dependent on red blood cell PLK (RBC - PLK) for its PLP requirements. Hence, if malaria parasites lack PLK and are dependent on the red cell PLK for their PLP requirements, then an individual with low RBC - PLK activity may be relatively resistant to malaria infection compared to one with high enzyme activity.

This study PLK activity in RBC haemolysate and corresponding parasite pellet from P.falciparum and P.berghei cultures has been measured. All the PLK activity expressed in PLP/L/min per 106 red blood cells was present in the RBC haemolysate and none in the parasites. Experiments performed in this investigation did not establish a positive correlation between PLK activity and parasite growth under in vitro conditions. Erythrocytes exhibiting high, intermediate and low PLK activity supported equivalent parasite growth rates in vitro. Low RBC-PLK activity could therefore be an innate resistance factor against P.falciparum in vivo but which cannot express it under in vitro conditions.