Purine and pyrimidine synthesis by the avian malaria parasite, Plasmodium lophurae.

Abstract

SYNOPSIS. Purine and pyrimidine biosynthesis in the avian malaria parasite Plasmodium lophurae and its host cell, the duck erythrocyte, were investigated in vitro. Pyrimidine synthesis, as measured by the incorporation of C14‐NaHCO3 into cytosine, uracil and thymine was slight in uninfected duck erythrocytes, whereas infected erythrocytes and erythrocyte‐free parasites had high rates of incorporation of NaHCO3 into these bases. In addition, orotidine‐5′‐monophosphate pyrophosphorylase and thymidylate synthetase, 2 enzymes of the pyrimidine biosynthetic pathway, were found in cell‐free extracts of the plasmodia. Purine synthesis was measured by determining the extent of incorporation of C14‐Na‐formate into adenine and guanine. Uninfected and infected erythrocytes had similar rates of Na‐formate incroporation into adenine. whereas free parasites incorporated little of this compound into adenine, or guanine. On the other hand, the incorporation of Na‐formate into guanine was 54% higher in infected erythrocytes than in uninfected erythrocytes.It is suggested that P. lophurae synthesizes purines to a limited extent, and derives most of its purines from the host erythrocyte. The greater incorporation of Na‐formate into guanine by infected cells, and its low incorporation into free parasites may be accounted for by parasite conversion of host cell adenine (in the form of ATP) into guanine. Pyrimidine biosynthesis in infected cells can be accounted for by de novo synthesis by the parasite itself.