Tritium labelling of amino sugars at C-2 by alkaline epimerization in tritiated water

Monitoring enzyme-catalyzed production of glucosamine-6P by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: a new enzymatic assay for glucosamine-6P synthase

A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) method for quantification of D-glucosamine-6P (GlcN-6P) that allows the kinetic study of glucosamine-6P synthase (Glms) is presented. The present report describes the optimization of the different steps of a new enzymatic assay for Glms based on in situ N-acetylation of GlcN-6P and MALDI-TOFMS analysis using N-(13C2)acetylglucosamine-6P as internal standard. Since no isotopically substituted GlcN-6P was available, the N-(13C2)acetyl derivative, easily obtained from (13C4)-acetic anhydride, was used as internal standard. Validation of the assay was achieved by measuring the fructose-6P Michaelis constant, in full agreement with reported values, and by studying the inhibition properties of arabinose-5P oxime.

Analysis of the Morgan-Elson chromogens by high-performance liquid chromatography

The Morgan-Elson method for quantitative N-acetylhexosamine analysis is a two-step procedure comprising alkali treatment of the sugar and subsequent condensation of the resulting chromogens with p-dimethylaminobenzaldehyde (Ehrlich's reagent) to yield a colored product. In the present investigation, the products formed in the first step of the procedure were analyzed by high-performance liquid chromatography (HPLC) on a reversed-phase (C18) column, which was eluted with a water-methanol gradient; the absorbance of the effluent was monitored at 229 nm. The profile generated from alkali-treated N-acetylglucosamine exhibited two major peaks, in a ratio of approximately 2.5:1, which accounted for 94% of the total peak area. A third peak, accounting for 3% of the peak area, was eluted in an intermediate position, and several smaller peaks were also observed. The three predominant components, isolated by preparative HPLC, all gave a purple color on addition of Ehrlich's reagent, indicating that they were Morgan-Elson chromogens. The HPLC profile of alkali-treated N-acetylmannosamine was identical to that of the products generated from N-actylglucosamine, as was expected because of the elimination of the asymmetry at C-2 during formation of the chromogens. N-Acetylgalactosamine yielded two major peaks, which were eluted in the same positions as the two major products formed from N-acetylglucosamine, but the intermediate peak seen in the N-acetylglucosamine pattern was absent. The HPLC procedure allowed detection of as little as approximately 25 ng of N-acetylglucosamine and may therefore be of value as an alternative to the complete Morgan-Elson procedure when only small amounts of sample are available for quantitative analysis.

Glucosamine 6-phosphate deaminase in Plasmodium falciparum

The pathways of glucose utilization for energy production in the malaria parasite, Plasmodium falciparum, have been studied extensively. Little is known, however, about the reactions by which glucose is converted into complex carbohydrates in the parasite, and knowledge of the catabolism of these substances is likewise scanty. The present investigation was undertaken to determine whether the parasites possess a key enzyme of glucosamine catabolism, i.e. glucosamine 6-phosphate deaminase (EC 5.3.1.40), which catalyses the conversion of the sugar phosphate to fructose 6-phosphate and ammonia. Lysates of Plasmodium-infected erythrocytes had substantially higher deaminase activity than control samples from normal erythrocytes, and an even higher specific activity was observed in extracts of isolated parasites, amounting to 20-40 times that of uninfected cells. Anion exchange chromatography indicated that the parasite deaminase eluted in a retarded position when compared to the elution profile of the erythrocyte enzyme. The charge difference suggested by these findings was established more directly by chromatofocusing, which indicated pI values of 6.85 and 8.55 for the parasite and erythrocyte deaminases, respectively. Other differences were also observed, notably a greater thermolability on the part of the parasite enzyme. These results indicated that the parasites synthesize a specific deaminase that is distinct from the normal erythrocyte enzyme. Studies on synchronized parasite cultures further indicated that the parasite deaminase is developmentally regulated, because a dramatic increase in activity levels occurred during the later stages of parasite development.

Glucosamine 6-phosphate deaminase in normal human erythrocytes

In the course of an investigation of hexosamine catabolism in the human malaria parasite, Plasmodium falciparum, it became apparent that a basic understanding of the relevant enzymatic reactions in the host erythrocyte is lacking. To acquire the necessary basic knowledge, we have determined the activities of several enzymes involved in hexosamine metabolism in normal human red blood cells. In the present communication we report the results of studies of glucosamine 6-phosphate deaminase (GlcN6-P) using a newly developed sensitive radiometric assay. The mean specific activity in extracts of fresh erythrocytes assayed within 4h of collection was 14.7 nmol/h/mg protein, whereas preparations from 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 Km of 41 microM. The metal chelators EDTA and EGTA were non-inhibitory; however, inhibition was observed in the presence of metal ions, especially Cu2+, Ni2+ and Zn2+. In addition, the deaminase was also inhibited by several sugar phosphates including the reaction product, fructose 6-phosphate.