GLUCOSAMINE 6-PHOSPHATE DEAMINASE IN NORMAL HUMAN ERYTHROCYTES

In the course of an investigation of hexosamine catabolism in the huma n malaria parasite, Plasmodium falciparum, it became apparent that a b asic understanding of the relevant enzymatic reactions in the host ery throcyte is lacking, To acquire the necessary basic knowledge, we have determined the activities of several enzymes involved in hexosamine m etabolism in normal human red blood cells, In the present communicatio n we report the results of studies of glucosamine 6-phosphate deaminas e (GlcN6-P) using a newly developed sensitive radiometric assay. The m ean specific activity in extracts of fresh erythrocytes assayed within 4 h of collection was 14.7 nmol/h/mg protein, whereas preparations fr om older erythrocytes that had been stored at 4 degrees C for up to 4 weeks had a mean specific activity of 6.2 nmol/h/mg, Characterization of the deaminase by chromatofocusing gave a pi of 8.55, The enzyme was optimally active at pH 9.0 and had a K-m of 41 mu M. The metal chelat ors EDTA and EGTA were non-inhibitory; however, inhibition was observe d in the presence of metal ions, especially Cu2+, Ni2+ and Zn2+. In ad dition, the deaminase was also inhibited by several sugar phosphates i ncluding the reaction product, fructose 6-phosphate.