N-ACETYLGLUCOSAMINE KINASE AND N-ACETYLGLUCOSAMINE 6-PHOSPHATE DEACETYLASE IN NORMAL HUMAN ERYTHROCYTES AND PLASMODIUM-FALCIPARUM

The major pathways of glucose metabolism in the malaria parasite, Plas modium falciparum, have now been elucidated, and the structures and pr operties of parasite-specific enzymes are presently being investigated . Little is known, however, about the enzymes catalysing monosaccharid e interconversions in the parasite. In the present investigation we ha ve examined the pathway of N-acetylglucosamine catabolism which, in hi gher organisms, involves the following reaction sequence: N-acetylgluc osamine --> N-acetylglucosamine 6-phosphate --> glucosamine 6-phosphat e --> fructose 6-phosphate. Assay of the specific kinase (E.C. 2.7.1.5 9) catalysing the phosphorylation of the sugar showed that the enzyme is present in Plasmodium extracts as well as in normal human erythrocy tes; specific activities of 7.2 and 5.3 nmol/h/mg protein were measure d for the parasite and erythrocyte extracts, respectively. N-Acetylglu cosamine 6-phosphate deacetylase (E.C. 3.5.1.25), catalysing the secon d reaction, was also detected in both normal and Plasmodium-infected e rythrocytes. At 75% parasitaemia, the deacetylase activity was close t o 3 times higher than that of normal control cells. The erythrocyte de acetylase was purified approximately 16000-fold by chromatography on D E52 cellulose, chromatofocusing, and size exclusion chromatography. At tempts to purify the parasite enzyme by the same procedures were unsuc cessful due to loss of activity. A partially purified erythrocyte deac etylase preparation (eluted from DE52 cellulose) had a pH optimum of 7 .5, a pI of 6.0, as indicated by chromatofocusing, and a K-m of 29 mu M. In conjunction with previous investigations, the present study indi cated that all three enzymes required for N-acetylglucosamine utilizat ion are present in Plasmodium parasites as well as in normal erythrocy tes.