Mutant/mutation
The mutant lacks expression of arginase.

Protein (function)
The protein shows high similarity to the metalloproteins arginase and agmatinase. A recombinant protein revealed strict specificity for arginine, and it has been proposed that its function in ornithine production is as a precursor for polyamine biosynthesis (Müller et al., 2005, Biol. Chem. 386, 117-26).  Extracellular arganine  is specifically converted by the parasite to ornithine.

Phenotype
The phenotype analyses indicate that arginase is not essential for asexual blood stage growth and multiplication. Mutant parasites did not convert arginine to ornithine. When blood stages were cultured ex vivo, wild type parasites exhibited high levels of ornithine generation, while ornithine generation by mutant parasites was indistinguishable from that of uninfected erythrocytes.

See also 28642498 and RMgm-4179 for a study using this mutant analysing liver stage development. Inthat study only liver stage development has been analysed. Evidence is presented that infectivity of part of the sporozoites is affected (see Additional Information in RMgm-4179)).

Additional information
A major metabolic activity of arginases in protozoa is the generation of ornithine for polyamine biosynthesis. However, this requirement seems unlikely to account for the high levels of observed activity of arginase in blood stages of Plasmodium because the vast majority of the metabolized arginine is excreted into the extracellular environment and not selectively retained in the cell. Moreover, the growth rate is not affected by the absence of arginine in the culture medium, suggesting that arginine is not rate-limiting for growth in vitro. The parasites lacking arginase presumably acquire sufficient amounts of ornithine either from the plasma or the activity of the host cell arginase.

Other mutants
RMgm-4179 - an independent mutant lacking expression of arginase